Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at beginning of period	$ 69,701	$ 64,170
Other comprehensive loss, net of tax	(392)	(332)
Balance at end of period	71,164	65,474
Net unrealized investment gains (losses)
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at beginning of period	1,214	774
Other comprehensive loss before reclassifications, net of tax	(400)	(394)
Amounts reclassified from accumulated other comprehensive loss, net of tax	14	83
Other comprehensive loss, net of tax	(386)	(311)
Balance at end of period	828	463
OCI before Reclass, pre-tax	(487)	(486)
Amounts reclassified, pre-tax	17	101
Foreign currency translation adjustments
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at beginning of period	7	4
Other comprehensive loss before reclassifications, net of tax	(2)	(12)
Other comprehensive loss, net of tax	(2)	(12)
Balance at end of period	5	(8)
Net cash flow hedges
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at beginning of period	248	279
Other comprehensive loss before reclassifications, net of tax	0	(5)
Amounts reclassified from accumulated other comprehensive loss, net of tax	(4)	(4)
Other comprehensive loss, net of tax	(4)	(9)
Balance at end of period	244	270
OCI before Reclass, pre-tax	0	(7)
Amounts reclassified, pre-tax	(5)	(6)
Amount expected to be reclassified	13
Pension and OPEB plans
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at beginning of period	(55)	(38)
Other comprehensive loss, net of tax	0	0
Balance at end of period	(55)	(38)
AOCI Including Portion Attributable to Noncontrolling Interest
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Balance at beginning of period	1,414	1,019
Balance at end of period	$ 1,022	$ 687