Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 968	$ 798	$ 2,415	$ 2,150
Net actuarial gains (losses) of defined benefit plans:
Adjustments	(17)	(33)	(47)	(43)
Recognized within Net income	12	13	39	40
Prior service (cost) credit of defined benefit plans:
Adjustments	0	20	1	20
Recognized within Net income	(1)	0	(3)	1
Derivative instruments:
Recognized within Net income	0	1	0	1
Other comprehensive income (loss)	(6)	1	(10)	19
Total comprehensive income	$ 962	$ 799	$ 2,405	$ 2,169