Accumulated Other Comprehensive Income (Other Comprehensive Income (Loss) Reclassification Adjustments) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Net holding (loss) gain on investment securities arising during the period, net of tax	$ (45)	$ 88	$ (378)	$ 297
Reclassification adjustment for net realized loss (gain) on investment securities, net of tax	9	(79)	25	(107)
Total reclassification adjustment on investments	(36)	9	(353)	190
Non-credit component of other-than-temporary impairments on investments, net of tax	(2)	0	(2)	4
Cash flow hedges, holding gain (loss), net of tax	2	(5)	34	(68)
Net change in unrecognized periodic benefit costs for defined benefit pension and postretirement benefit plans, net of tax	7	5	22	13
Foreign currency translation adjustment, net of tax	0	0	0	3
Net (loss) gain recognized in other comprehensive income, net of tax	$ (29)	$ 9	$ (299)	$ 142