Accumulated Other Comprehensive Income (Components of Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Other comprehensive income (loss) before tax
Net unrealized gain (loss)	$ (43)	$ 0	$ (184)	$ 81
Reclassification of net unrealized loss on securities transferred to held to maturity	0	0	0	227
Other reclassifications included in other revenue	0	0	0	(7)
Change in net unrealized gain (loss) on held to maturity securities:
Reclassification of net unrealized loss on securities transferred from available for sale	0	0	0	(227)
Amortization of amounts previously recorded upon transfer from available for sale	8	10	26	21
Other	0	0	0	(3)
Other comprehensive income (loss), before tax	(35)	10	(158)	92
Tax Effect
Net unrealized gain (loss)	11	0	45	(30)
Reclassification of net unrealized loss on securities transferred to held to maturity			0	(85)
Other reclassifications included in other revenue			0	3
Change in net unrealized gain (loss) on held to maturity securities:
Reclassification of net unrealized loss on securities transferred from available for sale (1)			0	85
Amortization of amounts previously recorded upon transfer from available for sale	(2)	(4)	(6)	(9)
Other			0	1
Other comprehensive income (loss)	9	(4)	39	(35)
Net of Tax
Net unrealized gain (loss)	(32)	0	(139)	51
Reclassification of net unrealized loss on securities transferred to held to maturity			0	142
Other reclassifications included in other revenue			0	(4)
Change in net unrealized gain (loss) on held to maturity securities:
Reclassification of net unrealized loss on securities transferred from available for sale			0	(142)
Amortization of amounts previously recorded upon transfer from available for sale	6	6	20	12
Other			0	(2)
Other comprehensive income (loss), net of tax	$ (26)	$ 6	$ (119)	$ 57