Other Comprehensive Income (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended						9 Months Ended
	Mar. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at beginning of period		$ 68,355	$ 65,474	$ 64,170	$ 61,599	$ 60,006	$ 58,543	$ 64,170	$ 58,543
Other comprehensive income (loss) before reclassifications, net of tax	$ (5)
Other comprehensive income (loss), net of tax		42	526	(332)	266	251	331	236	848
Balance at end of period	$ 65,474	69,112	68,355	65,474	62,933	61,599	60,006	69,112	62,933
Net unrealized investment gains (losses)
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at beginning of period		987		774	682		97	774	97
Other comprehensive income (loss) before reclassifications, net of tax		52			192			218	799
Amounts reclassified from accumulated other comprehensive loss, net of tax		(8)			(56)			39	(78)
Other comprehensive income (loss), net of tax		44			136			257	721
Balance at end of period		1,031	987		818	682		1,031	818
OCI before Reclass, pre-tax		83			214			278	933
Amounts reclassified, pre-tax		(10)			(63)			47	(93)
Foreign currency translation adjustments
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at beginning of period		(2)		4	(154)		(158)	4	(158)
Other comprehensive income (loss) before reclassifications, net of tax		1			(1)			(5)	3
Amounts reclassified from accumulated other comprehensive loss, net of tax		0			154			0	154
Other comprehensive income (loss), net of tax		1			153			(5)	157
Balance at end of period		(1)	(2)		(1)	(154)		(1)	(1)
Net cash flow hedges
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at beginning of period		267		279	305		312	279	312
Other comprehensive income (loss) before reclassifications, net of tax		0			(18)			(5)	(18)
Amounts reclassified from accumulated other comprehensive loss, net of tax		(3)			(5)			(10)	(12)
Other comprehensive income (loss), net of tax		(3)			(23)			(15)	(30)
Balance at end of period		264	267		282	305		264	282
Amount expected to be reclassified		15						15
OCI before Reclass, pre-tax		0			(25)			(7)	(25)
Amounts reclassified, pre-tax		(4)			(7)			(14)	(16)
Pension and OPEB plans
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at beginning of period		(39)		(38)	(149)		(149)	(38)	(149)
Other comprehensive income (loss) before reclassifications, net of tax		0			0			(6)	0
Amounts reclassified from accumulated other comprehensive loss, net of tax		0			0			5	0
Other comprehensive income (loss), net of tax		0			0			(1)	0
Balance at end of period		(39)	(39)		(149)	(149)		(39)	(149)
OCI before Reclass, pre-tax		0			0			(8)	0
Amounts reclassified, pre-tax		0			0			7	0
AOCI Including Portion Attributable to Noncontrolling Interest
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at beginning of period		1,213		$ 1,019	684		$ 102	1,019	102
Balance at end of period		$ 1,255	$ 1,213		$ 950	$ 684		$ 1,255	$ 950