Accumulated Other Comprehensive Income (Other Comprehensive Income (Loss) Reclassification Adjustments) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Net holding gain (loss) on investment securities arising during the period, net of tax	$ 237	$ (77)	$ 586	$ (333)
Reclassification adjustment for net realized loss (gain) on investment securities, net of tax	1	5	9	16
Total reclassification adjustment on investments	238	(72)	595	(317)
Non-credit component of other-than-temporary impairments on investments, net of tax	(1)	0	(1)	0
Cash flow hedges, holding gain (loss), net of tax	0	3	3	32
Net change in unrecognized periodic benefit costs for defined benefit pension and postretirement benefit plans, net of tax	3	8	6	15
Foreign currency translation adjustment, net of tax	0	(1)	0	0
Net gain (loss) recognized in other comprehensive income, net of tax	$ 240	$ (62)	$ 603	$ (270)