Accumulated Other Comprehensive Income (Loss) Accumulated Other Comprehensive Income Reclassification Adjustments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 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	$ (238)	$ (71)	$ (23)	$ (170)
Reclassification adjustment for net realized loss (gain) on investment securities, tax (benefit) expense	4	(1)	(5)	(2)
Tax (expense) benefit of non credit impairment on available-for-sale securities recognized in other comprehensive income (loss)	(2)	0	7	0
Cash flow hedges, holding gain (loss), tax (expense) benefit	(1)	0	(2)	0
Net change in unrecognized periodic benefit costs for defined benefit pension and postretirement benefit plans, tax expense	(4)	(1)	(7)	(2)
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax	0	0	0	0
Net gain (loss) recognized in other comprehensive income, tax (expense) benefit	$ (241)	$ (73)	$ (30)	$ (174)