Accumulated Other Comprehensive Loss Accumulated Other Comprehensive Income (Loss) Reclassification Adjustments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Change in net unrealized gains/losses on investments	$ 478	$ 695	$ (465)
Reclassification adjustment for net realized loss (gain) on investment securities, net of tax	(50)	(15)	47
Change in net unrealized gains (losses) on investments	428	680	(418)
Change in non-credit component of impairment losses on investments net of tax	0	0	(2)
Cash flow hedges, holding (loss) gain, net of tax	12	(16)	37
Net change in unrecognized periodic benefit costs for defined benefit pension and postretirement benefit plans, net of tax	(1)	26	(90)
Foreign currency translation adjustment, net of tax	7	0	(1)
Net gain (loss) recognized in other comprehensive loss, net of tax	$ 446	$ 690	$ (474)