Consolidated Statements of Comprehensive Income (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Net income	$ 884	$ 802	$ 1,682	$ 1,503
Other comprehensive income:
Change in amortization of accumulated actuarial losses, net of tax expense of $2 million, $0 million, $4 million and $2 million, respectively	(3)	(2)	(6)	(4)
Change in fuel hedge mark-to-market, net of tax benefit of $0 million, $2 million, $0 million and $7 million, respectively	0	(3)	0	(11)
Change in accumulated other comprehensive income of equity method investees	1	(1)	(1)	(3)
Other comprehensive income (loss), net of tax	4	(2)	5	(10)
Total comprehensive income	$ 888	$ 800	$ 1,687	$ 1,493