Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at beginning of period	$ 73,565	$ 71,164	$ 69,701	$ 68,355	$ 65,474	$ 64,170	$ 69,701	$ 64,170
Other comprehensive income (loss)	(93)	148	(392)	42	526	(332)	(337)	236
Balance at end of period	74,618	73,565	71,164	69,112	68,355	65,474	74,618	69,112
Net unrealized investment gains (losses)
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at beginning of period	977		1,214	987		774	1,214	774
Other Comprehensive income (loss) before reclassifications, net of tax	(61)			52			(297)	218
Amounts reclassified from accumulated other comprehensive loss, net of tax	(12)			(8)			(13)	39
Other comprehensive income (loss)	(73)			44			(310)	257
Balance at end of period	904	977		1,031	987		904	1,031
OCI before Reclass, pre-tax	(73)			83			(346)	278
Amounts reclassified, pre-tax	(14)			(10)			(15)	47
Foreign currency translation adjustments
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at beginning of period	6		7	(2)		4	7	4
Other Comprehensive income (loss) before reclassifications, net of tax	(5)			1			(6)	(5)
Other comprehensive income (loss)	(5)			1			(6)	(5)
Balance at end of period	1	6		(1)	(2)		1	(1)
Net cash flow hedges
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at beginning of period	241		248	267		279	248	279
Other Comprehensive income (loss) before reclassifications, net of tax	0			0			0	(5)
Amounts reclassified from accumulated other comprehensive loss, net of tax	(15)			(3)			(22)	(10)
Other comprehensive income (loss)	(15)			(3)			(22)	(15)
Balance at end of period	226	241		264	267		226	264
OCI before Reclass, pre-tax	0			0			0	(7)
Amounts reclassified, pre-tax	(20)			(4)			(29)	(14)
Amount expected to be reclassified	11						11
Pension and OPEB plans
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at beginning of period	(54)		(55)	(39)		(38)	(55)	(38)
Other Comprehensive income (loss) before reclassifications, net of tax	0			0			0	(6)
Amounts reclassified from accumulated other comprehensive loss, net of tax	0			0			1	5
Other comprehensive income (loss)	0			0			1	(1)
Balance at end of period	(54)	(54)		(39)	(39)		(54)	(39)
OCI before Reclass, pre-tax	0			0			0	(8)
Amounts reclassified, pre-tax	0			0			1	7
AOCI Including Portion Attributable to Noncontrolling Interest
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at beginning of period	1,170		$ 1,414	1,213		$ 1,019	1,414	1,019
Balance at end of period	$ 1,077	$ 1,170		$ 1,255	$ 1,213		$ 1,077	$ 1,255