Other Comprehensive Income (Loss) - Changes in AOCI by Component (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Jan. 01, 2018
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	$ 26,882	$ 34,569
Other comprehensive income (loss) before reclassification adjustments, pretax	218	25
Tax	3	(21)
Other comprehensive income (loss) before reclassification adjustments, net of taxes	221	4
Reclassification adjustments, pretax	(28)	145
Tax	6	(25)
Reclassification adjustments, net of taxes	(22)	120
Other comprehensive income (loss), net of taxes	199	124
Adoption of ASU 2018-02		(266)
Adoption of ASU 2016-01			$ (8)
Equity, ending balance	27,670	33,901
Derivatives
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	166	(108)
Other comprehensive income (loss) before reclassification adjustments, pretax	(13)	(181)
Tax	3	38
Other comprehensive income (loss) before reclassification adjustments, net of taxes	(10)	(143)
Reclassification adjustments, pretax	(48)	92
Tax	10	(19)
Reclassification adjustments, net of taxes	(38)	73
Other comprehensive income (loss), net of taxes	(48)	(70)
Adoption of ASU 2018-02		(23)
Adoption of ASU 2016-01			0
Equity, ending balance	118	(201)
Investments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	(78)	(61)
Other comprehensive income (loss) before reclassification adjustments, pretax	76	(112)
Tax	0	0
Other comprehensive income (loss) before reclassification adjustments, net of taxes	76	(112)
Reclassification adjustments, pretax	6	12
Tax	0	1
Reclassification adjustments, net of taxes	6	13
Other comprehensive income (loss), net of taxes	82	(99)
Adoption of ASU 2018-02		1
Adoption of ASU 2016-01			(8)
Equity, ending balance	4	(167)
Employee Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	(3,556)	(2,787)
Other comprehensive income (loss) before reclassification adjustments, pretax	(1)	(1)
Tax	6	3
Other comprehensive income (loss) before reclassification adjustments, net of taxes	5	2
Reclassification adjustments, pretax	14	41
Tax	(4)	(7)
Reclassification adjustments, net of taxes	10	34
Other comprehensive income (loss), net of taxes	15	36
Adoption of ASU 2018-02		(344)
Adoption of ASU 2016-01			0
Equity, ending balance	(3,541)	(3,095)
Cumulative Translation Adjustment
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	(2,077)	(1,954)
Other comprehensive income (loss) before reclassification adjustments, pretax	156	319
Tax	(6)	(62)
Other comprehensive income (loss) before reclassification adjustments, net of taxes	150	257
Reclassification adjustments, pretax	0	0
Tax	0	0
Reclassification adjustments, net of taxes	0	0
Other comprehensive income (loss), net of taxes	150	257
Adoption of ASU 2018-02		100
Adoption of ASU 2016-01			$ 0
Equity, ending balance	(1,927)	(1,597)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	(5,545)	(4,910)
Equity, ending balance	$ (5,346)	$ (5,060)

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

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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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