Other Comprehensive Income (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended
	Jul. 31, 2019	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Beginning of year balance		$ 64,170	$ 64,170	$ 58,543	$ 37,695
Other comprehensive income (loss) before reclassifications	$ (18)	(5)
Other comprehensive income (loss)			395	917	274
End of year balance			69,701	64,170	58,543
Net unrealized investment gains (losses)
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Beginning of year balance		774	774	97	0
Other comprehensive income (loss) before reclassifications			415	763	97
Amounts reclassified from accumulated other comprehensive loss, net of tax			25	(86)	0
Other comprehensive income (loss)			440	677	97
End of year balance			1,214	774	97
OCI before Reclass, pre-tax			497	927	132
Amounts reclassified, pre-tax			31	(105)	1
Foreign currency translation adjustments
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Beginning of year balance		4	4	(158)	(129)
Other comprehensive income (loss) before reclassifications			3	8	(29)
Amounts reclassified from accumulated other comprehensive loss, net of tax			0	154	0
Other comprehensive income (loss)			3	162	(29)
End of year balance			7	4	(158)
Net cash flow hedges
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Beginning of year balance		279	279	312	(15)
Adoption of new accounting standard			0	0	(3)
Other comprehensive income (loss) before reclassifications			(5)	(18)	344
Amounts reclassified from accumulated other comprehensive loss, net of tax			(26)	(15)	(14)
Other comprehensive income (loss)			(31)	(33)	330
End of year balance			248	279	312
OCI before Reclass, pre-tax			(7)	(25)	465
Amounts reclassified, pre-tax			(35)	(20)	(19)
Amount expected to be reclassified			13
Pension and OPEB plans
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Beginning of year balance		(38)	(38)	(149)	(21)
Adoption of new accounting standard			0	0	(4)
Other comprehensive income (loss) before reclassifications			(22)	120	(132)
Amounts reclassified from accumulated other comprehensive loss, net of tax			5	(9)	8
Other comprehensive income (loss)			(17)	111	(124)
End of year balance			(55)	(38)	(149)
OCI before Reclass, pre-tax			(30)	162	(178)
Amounts reclassified, pre-tax			7	(12)	11
AOCI Including Portion Attributable to Noncontrolling Interest
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Beginning of year balance		$ 1,019	1,019	102	(165)
Adoption of new accounting standard			0	0	(7)
End of year balance			$ 1,414	$ 1,019	$ 102