Accumulated Other Comprehensive Income (Other Comprehensive Income (Loss) Reclassification Adjustments) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) Reclassification Adjustments (Parantheticals) [Abstract]
Net holding gain (loss) on investment securities arising during the period, tax (expense) benefit	$ (160)	$ (198)	$ 133
Reclassification adjustment for net realized loss (gain) on investment securities, tax (benefit) expense	13	4	(13)
Non-credit component of other-than-temporary impairments on investments, tax (expense) benefit	0	0	1
Cash flow hedges, holding gain (loss), tax (expense) benefit	(3)	4	(10)
Net change in unrecognized periodic benefit costs for defined benefit pension and postretirement benefit plans, tax (expense) benefit	(2)	(9)	29
Foreign currency translation adjustment, tax (expense) benefit	(2)	0	0
Net gain (loss) realized in other comprehensive loss, tax (expense) benefit	$ (154)	$ (199)	$ 140