Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 1,056	$ 819	$ 2,053	$ 1,530
Net actuarial gains (losses) of defined benefit plans:
Adjustments	(3)	(18)	(15)	(30)
Recognized within Net income	11	13	23	27
Prior service (cost) credit of defined benefit plans:
Adjustments	0	1	0	1
Recognized within Net income	(1)	(1)	(2)	(2)
Other comprehensive income (loss)	7	(5)	6	(4)
Total comprehensive income	$ 1,063	$ 814	$ 2,059	$ 1,526