Accumulated Other Comprehensive Income (Other Comprehensive Income (Loss) Reclassification Adjustments) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 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	$ 152	$ 119	$ 182	$ 705
Reclassification adjustment for net realized loss (gain) on investment securities, net of tax	(39)	(3)	(28)	6
Total reclassification adjustment on investments	113	116	154	711
Change in non-credit component of impairment losses on investments net of tax	16	(1)	(6)	(2)
Cash flow hedges, holding gain (loss), net of tax	4	(34)	10	(31)
Net change in unrecognized periodic benefit costs for defined benefit pension and postretirement benefit plans, net of tax	8	4	25	10
Foreign currency translation adjustment, net of tax	1	(1)	1	(1)
Net gain (loss) recognized in other comprehensive income, net of tax	$ 142	$ 84	$ 184	$ 687