Other Comprehensive Income (Loss) - Changes in AOCI by Component (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance			$ 40,308	$ 44,767
Other comprehensive income (loss), net of taxes	$ 149	$ (166)	281	(104)
Equity, ending balance	38,499	43,957	38,499	43,957
Derivatives
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	(37)	111	338	404
Other comprehensive income (loss) before reclassification adjustments, pretax	(88)	(69)	(520)	(311)
Tax	31	24	182	109
Other comprehensive income (loss) before reclassification adjustments, net of taxes	(57)	(45)	(338)	(202)
Reclassification adjustments, pretax	(14)	(45)	(159)	(254)
Tax	5	16	56	89
Reclassification adjustments, net of taxes	(9)	(29)	(103)	(165)
Other comprehensive income (loss), net of taxes	(66)	(74)	(441)	(367)
Equity, ending balance	(103)	37	(103)	37
Investments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	75	167	(3)	41
Other comprehensive income (loss) before reclassification adjustments, pretax	170	(22)	283	108
Tax	(19)	(3)	(23)	8
Other comprehensive income (loss) before reclassification adjustments, net of taxes	151	(25)	260	116
Reclassification adjustments, pretax	(24)	(5)	(73)	(26)
Tax	8	0	26	6
Reclassification adjustments, net of taxes	(16)	(5)	(47)	(20)
Other comprehensive income (loss), net of taxes	135	(30)	213	96
Equity, ending balance	210	137	210	137
Employee Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	(3,133)	(2,543)	(3,206)	(2,407)
Other comprehensive income (loss) before reclassification adjustments, pretax	2	(177)	27	(395)
Tax	(13)	21	(7)	88
Other comprehensive income (loss) before reclassification adjustments, net of taxes	(11)	(156)	20	(307)
Reclassification adjustments, pretax	31	11	86	25
Tax	(7)	1	(20)	2
Reclassification adjustments, net of taxes	24	12	66	27
Other comprehensive income (loss), net of taxes	13	(144)	86	(280)
Equity, ending balance	(3,120)	(2,687)	(3,120)	(2,687)
Cumulative Translation Adjustment
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	(1,999)	(1,821)	(2,355)	(2,186)
Other comprehensive income (loss) before reclassification adjustments, pretax	23	70	261	424
Tax	44	12	162	23
Other comprehensive income (loss) before reclassification adjustments, net of taxes	67	82	423	447
Reclassification adjustments, pretax	0	0	0	0
Tax	0	0	0	0
Reclassification adjustments, net of taxes	0	0	0	0
Other comprehensive income (loss), net of taxes	67	82	423	447
Equity, ending balance	(1,932)	(1,739)	(1,932)	(1,739)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	(5,094)	(4,086)	(5,226)	(4,148)
Other comprehensive income (loss) before reclassification adjustments, pretax	107	(198)	51	(174)
Tax	43	54	314	228
Other comprehensive income (loss) before reclassification adjustments, net of taxes	150	(144)	365	54
Reclassification adjustments, pretax	(7)	(39)	(146)	(255)
Tax	6	17	62	97
Reclassification adjustments, net of taxes	(1)	(22)	(84)	(158)
Other comprehensive income (loss), net of taxes	149	(166)	281	(104)
Equity, ending balance	$ (4,945)	$ (4,252)	$ (4,945)	$ (4,252)