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Other Comprehensive Income (Loss) - Changes in AOCI by Component (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2018
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	$ 32,766	$ 39,712	$ 34,569	$ 40,308
Other comprehensive income (loss) before reclassification adjustments, pretax	(110)	107	(143)	51
Tax	5	43	(130)	314
Other comprehensive income (loss) before reclassification adjustments, net of taxes	(105)	150	(273)	365
Reclassification adjustments, pretax	84	(7)	365	(146)
Tax	(8)	6	(59)	62
Reclassification adjustments, net of taxes	76	(1)	306	(84)
Other comprehensive income (loss), net of taxes	(29)	149	33	281
Adoption of ASU 2018-02 (see Note 1)			(266)
Equity, ending balance	32,656	38,499	32,656	38,499
Derivatives
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	65	(37)	(108)	338
Other comprehensive income (loss) before reclassification adjustments, pretax	29	(88)	113	(520)
Tax	(6)	31	(24)	182
Other comprehensive income (loss) before reclassification adjustments, net of taxes	23	(57)	89	(338)
Reclassification adjustments, pretax	5	(14)	169	(159)
Tax	(1)	5	(35)	56
Reclassification adjustments, net of taxes	4	(9)	134	(103)
Other comprehensive income (loss), net of taxes	27	(66)	223	(441)
Adoption of ASU 2018-02 (see Note 1)			(23)
Adoption of ASU 2016-01 (see Note 1)					$ 0
Equity, ending balance	92	(103)	92	(103)
Investments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	(164)	75	(61)	(3)
Other comprehensive income (loss) before reclassification adjustments, pretax	8	170	(125)	283
Tax	0	(19)	1	(23)
Other comprehensive income (loss) before reclassification adjustments, net of taxes	8	151	(124)	260
Reclassification adjustments, pretax	32	(24)	68	(73)
Tax	0	8	0	26
Reclassification adjustments, net of taxes	32	(16)	68	(47)
Other comprehensive income (loss), net of taxes	40	135	(56)	213
Adoption of ASU 2018-02 (see Note 1)			1
Adoption of ASU 2016-01 (see Note 1)					(8)
Equity, ending balance	(124)	210	(124)	210
Employee Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	(3,065)	(3,133)	(2,787)	(3,206)
Other comprehensive income (loss) before reclassification adjustments, pretax	0	2	(2)	27
Tax	0	(13)	4	(7)
Other comprehensive income (loss) before reclassification adjustments, net of taxes	0	(11)	2	20
Reclassification adjustments, pretax	47	31	128	86
Tax	(7)	(7)	(24)	(20)
Reclassification adjustments, net of taxes	40	24	104	66
Other comprehensive income (loss), net of taxes	40	13	106	86
Adoption of ASU 2018-02 (see Note 1)			(344)
Adoption of ASU 2016-01 (see Note 1)					0
Equity, ending balance	(3,025)	(3,120)	(3,025)	(3,120)
Cumulative Translation Adjustment
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	(1,958)	(1,999)	(1,954)	(2,355)
Other comprehensive income (loss) before reclassification adjustments, pretax	(147)	23	(129)	261
Tax	11	44	(111)	162
Other comprehensive income (loss) before reclassification adjustments, net of taxes	(136)	67	(240)	423
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	(136)	67	(240)	423
Adoption of ASU 2018-02 (see Note 1)			100
Adoption of ASU 2016-01 (see Note 1)					0
Equity, ending balance	(2,094)	(1,932)	(2,094)	(1,932)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Equity, beginning balance	(5,122)	(5,094)	(4,910)	(5,226)
Adoption of ASU 2016-01 (see Note 1)					$ (8)
Equity, ending balance	$ (5,151)	$ (4,945)	$ (5,151)	$ (4,945)

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

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