Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 2,986	$ 2,821	$ 2,162
Net actuarial gains (losses) of defined benefit plans:
Adjustment, net of tax benefit (expense) of $36, $25 and ($60)	(74)	(46)	105
Recognized within Net income, net of tax benefit (expense) of ($25), ($21) and ($37)	53	42	71
Prior service (cost) credit of defined benefit plans:
Adjustment, net of tax benefit (expense) of ($11), $0 and $1	20	(1)	(3)
Recognized within Net income, net of tax benefit (expense) of $0, $0 and $2	0	0	(3)
Derivative instruments:
Recognized within Net income, net of tax benefit (expense) of ($1), ($1) and ($1)	1	1	1
Other comprehensive income (loss), net of taxes	0	(4)	171
Total comprehensive income	$ 2,986	$ 2,817	$ 2,333