Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Beginning of year balance	$ 64,170	$ 69,701	$ 64,170	$ 58,543
Other comprehensive income (loss) before reclassifications	(5)
Other comprehensive income (loss)		(449)	395	917
End of year balance		75,381	69,701	64,170
Net unrealized investment gains (losses)
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Beginning of year balance	774	1,214	774	97
Other comprehensive income (loss) before reclassifications		(410)	415	763
Amounts reclassified from accumulated other comprehensive loss, net of tax		(26)	25	(86)
Other comprehensive income (loss)		(436)	440	677
End of year balance		778	1,214	774
OCI before Reclass, pre-tax		(489)	497	927
Amounts reclassified, pre-tax		(32)	31	(105)
Foreign currency translation adjustments
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Beginning of year balance	4	7	4	(158)
Other comprehensive income (loss) before reclassifications		(7)	3	8
Amounts reclassified from accumulated other comprehensive loss, net of tax		0	0	154
Other comprehensive income (loss)		(7)	3	162
End of year balance		0	7	4
Net cash flow hedges
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Beginning of year balance	279	248	279	312
Other comprehensive income (loss) before reclassifications		0	(5)	(18)
Amounts reclassified from accumulated other comprehensive loss, net of tax		(26)	(26)	(15)
Other comprehensive income (loss)		(26)	(31)	(33)
End of year balance		222	248	279
OCI before Reclass, pre-tax		0	(7)	(25)
Amounts reclassified, pre-tax		(34)	(35)	(20)
Amount expected to be reclassified		11
Pension and OPEB plans
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Beginning of year balance	(38)	(55)	(38)	(149)
Other comprehensive income (loss) before reclassifications		15	(22)	120
Amounts reclassified from accumulated other comprehensive loss, net of tax		5	5	(9)
Other comprehensive income (loss)		20	(17)	111
End of year balance		(35)	(55)	(38)
OCI before Reclass, pre-tax		20	(30)	162
Amounts reclassified, pre-tax		6	7	(12)
AOCI Including Portion Attributable to Noncontrolling Interest
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Beginning of year balance	$ 1,019	1,414	1,019	102
End of year balance		$ 965	$ 1,414	$ 1,019