Accumulated Other Comprehensive Income (Loss) Accumulated Other Comprehensive Income Reclassification Adjustments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss) Reclassification Adjustments (Parantheticals) [Abstract]
Net holding gain (loss) on investment securities arising during the period, tax (expense) benefit	$ (43)	$ (35)	$ (68)	$ (205)
Reclassification adjustment for net realized loss (gain) on investment securities, tax (benefit) expense	10	1	7	(1)
Tax (expense) benefit of non credit impairment on available-for-sale securities recognized in other comprehensive income (loss)	(5)	0	2	0
Cash flow hedges, holding gain (loss), tax (expense) benefit	0	(2)	(2)	(2)
Net change in unrecognized periodic benefit costs for defined benefit pension and postretirement benefit plans, tax expense	(2)	(1)	(9)	(3)
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax	(1)	0	(1)	0
Net gain (loss) recognized in other comprehensive income, tax (expense) benefit	$ (41)	$ (37)	$ (71)	$ (211)