Consolidated statements of comprehensive income (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Statement of Comprehensive Income [Abstract]
Net income	$ 629	$ 784	$ 1,651	$ 1,495
Available-for-sale investments:
Unrealized gains (losses), net of taxes	0	1	0	3
Net actuarial gains (losses) of defined benefit plans:
Adjustment, net of taxes	6	(3)	86	8
Reclassification of recognized transactions, net of taxes	13	128	46	151
Prior service cost of defined benefit plans:
Adjustment, net of taxes	0	0	(2)	0
Reclassification of recognized transactions, net of taxes	(1)	0	(3)	0
Derivative instrument:
Change in fair value, net of taxes	0	(3)	(1)	(3)
Reclassification of recognized transactions, net of taxes	0	0	1	0
Other comprehensive income (loss), net of taxes	18	123	127	159
Total comprehensive income	$ 647	$ 907	$ 1,778	$ 1,654