Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions		1 Months Ended	3 Months Ended						9 Months Ended
		Jul. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Jan. 01, 2018
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at beginning of period		$ 61,599	$ 61,599	$ 60,006	$ 58,543	$ 35,611	$ 38,677	$ 37,695	$ 58,543	$ 37,695
Other comprehensive income (loss) before reclassifications, net of tax		18
Adoption of new accounting standard	[1]										$ (13)
Other comprehensive income (loss), net of tax			266	251	331	(12)	(31)	344	848	301
Balance at end of period			62,933	61,599	60,006	36,622	35,611	38,677	62,933	36,622
Net unrealized investment gains (losses)
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at beginning of period		682	682		97	0		0	97	0
Other comprehensive income (loss) before reclassifications, net of tax			192			0			799	0
Amounts reclassified from accumulated other comprehensive loss, net of tax			(56)			0			(78)	0
Other comprehensive income (loss), net of tax			136			0			721	0
Balance at end of period			818	682		0	0		818	0
OCI before Reclass, pre-tax			214			0			933	0
Amounts reclassified, pre-tax			(63)			0			(93)	0
Foreign currency translation adjustments
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at beginning of period		(154)	(154)		(158)	(155)		(129)	(158)	(129)
Other comprehensive income (loss) before reclassifications, net of tax			(1)			(8)			3	(34)
Amounts reclassified from accumulated other comprehensive loss, net of tax			154			0			154	0
Other comprehensive income (loss), net of tax			153			(8)			157	(34)
Balance at end of period			(1)	(154)		(163)	(155)		(1)	(163)
Net cash flow hedges
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at beginning of period		305	305		312	321		(15)	312	(15)
Other comprehensive income (loss) before reclassifications, net of tax			(18)			0			(18)	344
Amounts reclassified from accumulated other comprehensive loss, net of tax			(5)			(4)			(12)	(9)
Adoption of new accounting standard											(3)
Other comprehensive income (loss), net of tax			(23)			(4)			(30)	335
Balance at end of period			282	305		317	321		282	317
Amount expected to be reclassified			15						15
OCI before Reclass, pre-tax			(25)			0			(25)	464
Amounts reclassified, pre-tax			(7)			(5)			(16)	(12)
Pension and OPEB plans
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at beginning of period		(149)	(149)		(149)	(25)		(21)	(149)	(21)
Adoption of new accounting standard											(4)
Balance at end of period			(149)	(149)		(25)	(25)		(149)	(25)
AOCI Including Portion Attributable to Noncontrolling Interest
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at beginning of period		$ 684	684		$ 102	141		$ (165)	102	(165)
Balance at end of period			$ 950	$ 684		$ 129	$ 141		$ 950	$ 129
Accounting Standards Update 2018-02
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Adoption of new accounting standard											$ (7)

[1] Reflects the adoption of Accounting Standards Update (“ASU”) 2014-09, Revenue from Contracts with Customers, which resulted in a reduction to retained earnings of $13 million and the adoption of ASU 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income, which resulted in a reduction to accumulated other comprehensive income of $7 million and an increase to retained earnings of $7 million, each during the three months ended March 31, 2018.