Other Comprehensive Income (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jul. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Beginning of year balance		$ 58,543	$ 37,695	$ 36,834
Other comprehensive income (loss) before reclassifications	$ (18)
Other comprehensive income (loss)		917	274	140
End of year balance		64,170	58,543	37,695
Net unrealized investment gains (losses)
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Beginning of year balance		97	0	0
Other comprehensive income (loss) before reclassifications		763	97	0
Amounts reclassified from accumulated other comprehensive loss, net of tax		(86)	0	0
Other comprehensive income (loss)		677	97	0
End of year balance		774	97	0
OCI before Reclass, pre-tax		927	132	0
Amounts reclassified, pre-tax		(105)	1	0
Foreign currency translation adjustments
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Beginning of year balance		(158)	(129)	(127)
Other comprehensive income (loss) before reclassifications		8	(29)	(2)
Amounts reclassified from accumulated other comprehensive loss, net of tax		154	0	0
Other comprehensive income (loss)		162	(29)	(2)
End of year balance		4	(158)	(129)
Net cash flow hedges
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Beginning of year balance		312	(15)	(5)
Adoption of new accounting standard			(3)
Other comprehensive income (loss) before reclassifications		(18)	344	(11)
Amounts reclassified from accumulated other comprehensive loss, net of tax		(15)	(14)	1
Other comprehensive income (loss)		(33)	330	(10)
End of year balance		279	312	(15)
OCI before Reclass, pre-tax		(25)	465	(18)
Amounts reclassified, pre-tax		(20)	(19)	2
Amount expected to be reclassified		14
Pension and OPEB plans
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Beginning of year balance		(149)	(21)	(173)
Adoption of new accounting standard			(4)
Other comprehensive income (loss) before reclassifications		120	(132)	0
Amounts reclassified from accumulated other comprehensive loss, net of tax		(9)	8	152
Other comprehensive income (loss)		111	(124)	152
End of year balance		(38)	(149)	(21)
OCI before Reclass, pre-tax		162	(178)	0
Amounts reclassified, pre-tax		(12)	11	249
AOCI Including Portion Attributable to Noncontrolling Interest
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Beginning of year balance		102	(165)	(305)
Adoption of new accounting standard			(7)
End of year balance		$ 1,019	$ 102	$ (165)