SCHEDULE 13G

Amendment No. 3 
UAL Corporation 
Common Stock 
Cusip #902549807 


Cusip #902549807 
Item 1:	Reporting Person - FMR LLC
Item 4:	Delaware
Item 5:	0 
Item 6:	0 
Item 7:	13,783,380 
Item 8:	0 
Item 9:	13,783,380 
Item 11:	9.469% 
Item 12:	    HC


Cusip #902549807  
Item 1:	Reporting Person - Edward C. Johnson 3d 
Item 4:	United States of America
Item 5:	0 
Item 6:	0 
Item 7:	13,783,380 
Item 8:	0 
Item 9:	13,783,380 
Item 11:	9.469% 
Item 12:	IN 




	SCHEDULE 13G - TO BE INCLUDED IN 
STATEMENTS
	FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b)



Item 1(a).	Name of Issuer:	

		UAL Corporation 

Item 1(b).	Name of Issuer's Principal Executive Offices:

		John Lakosil - WHQLD
		77 W Wacker 
		Chicago, IL  60601
		  

Item 2(a).	Name of Person Filing: 

		FMR LLC

Item 2(b).	Address or Principal Business Office or, if None, 
Residence:

		82 Devonshire Street, Boston, 
Massachusetts  02109

Item 2(c).	Citizenship:

		Not applicable

Item 2(d).	Title of Class of Securities:

		Common Stock 

Item 2(e).	CUSIP Number:  

		902549807 

Item 3.	This statement is filed pursuant to Rule 13d-1(b) or 13d-2(b) 
and the person filing, FMR LLC, is a parent holding company 
in accordance with Section 240.13d-1(b)(ii)(G).  (Note:  See 
Item 7).

Item 4.	Ownership

	(a)	Amount Beneficially Owned:	13,783,380 

	(b)	Percent of Class:	9.469% 

	(c)	Number of shares as to which such 
person has:  

	(i)	sole power to vote or to direct 
the vote:	0 

	(ii)	shared power to vote or to 
direct the vote:	0 

	(iii)	sole power to dispose or to 
direct the disposition of:	13,783,380 

	(iv)	shared power to dispose or to 
direct the disposition of:	0 



Item 5.	Ownership of Five Percent or Less of a Class.

	Not applicable.

Item 6.	Ownership of More than Five Percent on Behalf of Another 
Person.

	Various persons have the right to receive or the power to 
direct the receipt of dividends from, or the proceeds from the 
sale of, the Common Stock of UAL Corporation.  No one 
person's interest in the Common Stock of UAL Corporation is 
more than five percent of the total outstanding Common 
Stock.

Item 7.	Identification and Classification of the Subsidiary Which 
Acquired the Security Being Reported on By the Parent 
Holding Company.

	See attached Exhibit A. 

Item 8.	Identification and Classification of Members of 
the Group.

	Not applicable.  See attached Exhibit A. 

Item 9.	Notice of Dissolution of Group.

	Not applicable.

Item 10.	Certification.

	By signing below I certify that, to the best of my knowledge 
and belief, the securities referred to above were acquired in the 
ordinary course of business and were not acquired for the 
purpose of and do not have the effect of changing or 
influencing the control of the issuer of such securities and 
were not acquired in connection with or as a participant in any 
transaction having such purpose or effect.

Signature

	After reasonable inquiry and to the best of my knowledge and 
belief, I certify that the information set forth in this statement 
is true, complete and correct. 

July 09, 2009 			
Date

 /s/ Scott C. Goebel			
Signature

Scott C. Goebel			
Duly authorized under Power of Attorney
effective as of June 1, 2008 by and on behalf of FMR LLC 
and its direct and indirect  subsidiaries


	SCHEDULE 13G - TO BE INCLUDED IN 
STATEMENTS
	FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b)



	Pursuant to the instructions in Item 7 of Schedule 13G, 
Fidelity Management & Research Company ("Fidelity"), 82 
Devonshire Street, Boston, Massachusetts 02109, a wholly-
owned subsidiary of FMR LLC and an investment adviser 
registered under Section 203 of the Investment Advisers Act 
of 1940, is the beneficial owner of 13,783,380 shares or 
9.469% of the Common Stock outstanding of UAL 
Corporation  ("the Company") as a result of acting as 
investment adviser to various investment companies registered 
under Section 8 of the Investment Company Act of 1940. The 
number of shares of Common Stock of UAL Corporation 
owned by the investment companies at June 30, 2009 included 
1,634,440 shares of Common Stock resulting from the 
assumed conversion of $53,340,000 principal amount of UAL 
CORP CONV 4.5% 6/30/21 (30.6419 shares of Common 
Stock for each $1,000 principal amount of debenture).

	Edward C. Johnson 3d and FMR LLC, through its 
control of Fidelity, and the funds each has sole power to 
dispose of the 13,783,380 shares owned by the Funds.

	Members of the family of Edward C. Johnson 3d, 
Chairman of FMR LLC, are the predominant owners, directly 
or through trusts, of Series B voting common shares of FMR 
LLC, representing 49% of the voting power of FMR LLC.  
The Johnson family group and all other Series B shareholders 
have entered into a shareholders' voting agreement under 
which all Series B voting common shares will be voted in 
accordance with the majority vote of Series B voting common 
shares.  Accordingly, through their ownership of voting 
common shares and the execution of the shareholders' voting 
agreement, members of the Johnson family may be deemed, 
under the Investment Company Act of 1940, to form a 
controlling group with respect to FMR LLC.

	Neither FMR LLC nor Edward C. Johnson 3d, 
Chairman of FMR LLC, has the sole power to vote or direct 
the voting of the shares owned directly by the Fidelity Funds, 
which power resides with the Funds' Boards of Trustees.  
Fidelity carries out the voting of the shares under written 
guidelines established by the Funds' Boards of Trustees.



	SCHEDULE 13G - TO BE INCLUDED IN 
STATEMENTS
	FILED PURSUANT TO RULE 13d-1(b) or 13d-2(b)
	RULE 13d-1(f)(1)  AGREEMENT

	The undersigned persons, on July 09, 2009, agree and 
consent to the joint filing on their behalf of this Schedule 13G 
in connection with their beneficial ownership of the Common 
Stock of UAL Corporation at June 30, 2009.

	FMR LLC

	By /s/ Scott C. Goebel			
	Scott C. Goebel
	Duly authorized under Power of Attorney effective as 
of June 1, 2008, by and on behalf of FMR LLC and its direct 
and indirect subsidiaries

	Edward C. Johnson 3d

	By /s/ Scott C. Goebel			
	Scott C. Goebel
	Duly authorized under Power of Attorney effective as 
of June 1, 2008, by and on behalf of Edward C. Johnson 3d

	Fidelity Management & Research Company

	By /s/ Scott C. Goebel			
	Scott C. Goebel
	Senior V.P. and General Counsel