Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at beginning of period	$ 71,164	$ 69,701	$ 65,474	$ 64,170	$ 69,701	$ 64,170
Other comprehensive income (loss)	148	(392)	526	(332)	(244)	194
Balance at end of period	73,565	71,164	68,355	65,474	73,565	68,355
Net unrealized investment gains (losses)
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at beginning of period	828	1,214	463	774	1,214	774
Other Comprehensive income (loss) before reclassifications, net of tax	164		560		(236)	166
Amounts reclassified from accumulated other comprehensive loss, net of tax	(15)		(36)		(1)	47
Other comprehensive income (loss)	149		524		(237)	213
Balance at end of period	977	828	987	463	977	987
OCI before Reclass, pre-tax	214		681		(273)	195
Amounts reclassified, pre-tax	(18)		(44)		(1)	57
Foreign currency translation adjustments
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at beginning of period	5	7	(8)	4	7	4
Other Comprehensive income (loss) before reclassifications, net of tax	1		6		(1)	(6)
Other comprehensive income (loss)	1		6		(1)	(6)
Balance at end of period	6	5	(2)	(8)	6	(2)
Net cash flow hedges
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at beginning of period	244	248	270	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	(3)		(3)		(7)	(7)
Other comprehensive income (loss)	(3)		(3)		(7)	(12)
Balance at end of period	241	244	267	270	241	267
OCI before Reclass, pre-tax	0		0		0	(7)
Amounts reclassified, pre-tax	(4)		(4)		(9)	(10)
Amount expected to be reclassified	13				13
Pension and OPEB plans
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at beginning of period	(55)	(55)	(38)	(38)	(55)	(38)
Other Comprehensive income (loss) before reclassifications, net of tax	0		(6)		0	(6)
Amounts reclassified from accumulated other comprehensive loss, net of tax	1		5		1	5
Other comprehensive income (loss)	1		(1)		1	(1)
Balance at end of period	(54)	(55)	(39)	(38)	(54)	(39)
OCI before Reclass, pre-tax	0		(8)		0	(8)
Amounts reclassified, pre-tax	1		7		1	7
AOCI Including Portion Attributable to Noncontrolling Interest
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at beginning of period	1,022	1,414	687	1,019	1,414	1,019
Balance at end of period	$ 1,170	$ 1,022	$ 1,213	$ 687	$ 1,170	$ 1,213