Accumulated Other Comprehensive Income (Loss) Accumulated Other Comprehensive Income Reclassification Adjustments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Accumulated Other Comprehensive Income (Loss) Reclassification Adjustments (Parantheticals) [Abstract]
Net holding gain (loss) on investment securities arising during the period, tax (expense) benefit	$ (71)	$ 21	$ (170)	$ 98
Reclassification adjustment for net realized loss (gain) on investment securities, tax (benefit) expense	(1)	(1)	(2)	(4)
Cash flow hedges, holding gain (loss), tax (expense) benefit	0	(1)	0	(9)
Net change in unrecognized periodic benefit costs for defined benefit pension and postretirement benefit plans, tax expense	(1)	(2)	(2)	(5)
Net gain (loss) recognized in other comprehensive income, tax (expense) benefit	$ (73)	$ 17	$ (174)	$ 80