Other Comprehensive Income (Loss) - Changes in AOCI by Component (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	$ 34,569	$ 40,308
Other comprehensive income (loss) before reclassification adjustments, pretax	25	83
Tax	(21)	140
Other comprehensive income (loss) before reclassification adjustments, net of taxes	4	223
Reclassification adjustments, pretax	145	(124)
Tax	(25)	47
Reclassification adjustments, net of taxes	120	(77)
Other comprehensive income (loss), net of taxes	124	146
Reclassification of provisional stranded tax effects	(266)
Adoption of ASU 2016-01			$ (8)
Equity, ending balance	33,901	40,088
Derivatives
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	(108)	338
Other comprehensive income (loss) before reclassification adjustments, pretax	(181)	(263)
Tax	38	92
Other comprehensive income (loss) before reclassification adjustments, net of taxes	(143)	(171)
Reclassification adjustments, pretax	92	(95)
Tax	(19)	34
Reclassification adjustments, net of taxes	73	(61)
Other comprehensive income (loss), net of taxes	(70)	(232)
Reclassification of provisional stranded tax effects	(23)
Adoption of ASU 2016-01			0
Equity, ending balance	(201)	106
Investments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	(61)	(3)
Other comprehensive income (loss) before reclassification adjustments, pretax	(112)	87
Tax	0	(7)
Other comprehensive income (loss) before reclassification adjustments, net of taxes	(112)	80
Reclassification adjustments, pretax	12	(57)
Tax	1	20
Reclassification adjustments, net of taxes	13	(37)
Other comprehensive income (loss), net of taxes	(99)	43
Reclassification of provisional stranded tax effects	1
Adoption of ASU 2016-01			(8)
Equity, ending balance	(167)	40
Employee Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	(2,787)	(3,206)
Other comprehensive income (loss) before reclassification adjustments, pretax	(1)	(4)
Tax	3	9
Other comprehensive income (loss) before reclassification adjustments, net of taxes	2	5
Reclassification adjustments, pretax	41	28
Tax	(7)	(7)
Reclassification adjustments, net of taxes	34	21
Other comprehensive income (loss), net of taxes	36	26
Reclassification of provisional stranded tax effects	(344)
Adoption of ASU 2016-01			0
Equity, ending balance	(3,095)	(3,180)
Cumulative Translation Adjustment
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	(1,954)	(2,355)
Other comprehensive income (loss) before reclassification adjustments, pretax	319	263
Tax	(62)	46
Other comprehensive income (loss) before reclassification adjustments, net of taxes	257	309
Reclassification adjustments, pretax	0	0
Tax	0	0
Reclassification adjustments, net of taxes	0	0
Other comprehensive income (loss), net of taxes	257	309
Reclassification of provisional stranded tax effects	100
Adoption of ASU 2016-01			$ 0
Equity, ending balance	(1,597)	(2,046)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	(4,910)	(5,226)
Equity, ending balance	$ (5,060)	$ (5,080)

Tax Cuts and Jobs Act, Reclassification From AOCI to Retained Earnings, Tax Effect

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.

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