Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 3,682	$ 3,595	$ 2,986
Net actuarial losses of defined benefit plans:
Adjustment, net of tax effect of ($26), $6 and $36	92	(43)	(74)
Recognized within Net income, net of tax effect of ($27), ($25) and ($25)	56	51	53
Prior service credit of defined benefit plans:
Adjustment, net of tax effect of $1, $0 and ($11)	(2)	0	20
Recognized within Net income, net of tax effect of $1, $2 and $0	(5)	(3)	0
Derivative instruments:
Recognized within Net income, net of tax effect of $0, $0 and ($1)	1	1	1
Other comprehensive income (loss), net of taxes	142	6	0
Total comprehensive income	$ 3,824	$ 3,601	$ 2,986