Accumulated Other Comprehensive Income (Other Comprehensive Income (Loss) Reclassification Adjustments) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Net holding gain (loss) on investment securities arising during the period, net of tax	$ (716)	$ 350
Reclassification adjustment for net realized loss (gain) on investment securities, net of tax	27	7
Total reclassification adjustment on investments	(689)	357
Non-credit component of other-than-temporary impairments on investments, net of tax	(32)	0
Cash flow hedges, holding gain (loss), net of tax	3	3
Net change in unrecognized periodic benefit costs for defined benefit pension and postretirement benefit plans, net of tax	7	3
Foreign currency translation adjustment, net of tax	(1)	0
Net gain (loss) recognized in other comprehensive income, net of tax	$ (712)	$ 363