Accumulated Other Comprehensive Income (Components of Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Other comprehensive income (loss) before tax
Net unrealized gain (loss)	$ 0	$ 77	$ 81	$ 266
Reclassification of net unrealized loss on securities transferred to held to maturity	0	0	227	0
Other reclassifications included in other revenue	0	0	(7)	(3)
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	(227)	0
Amortization of amounts previously recorded upon transfer from available for sale	10	0	21	0
Other	0	0	(3)	1
Other comprehensive income (loss), before tax	10	77	92	264
Tax Effect
Net unrealized gain (loss)	0	(29)	(30)	(100)
Reclassification of net unrealized loss on securities transferred to held to maturity			(85)	0
Other reclassifications included in other revenue	0	0	3	1
Change in net unrealized gain (loss) on held to maturity securities:
Reclassification of net unrealized loss on securities transferred from available for sale (1)			85	0
Amortization of amounts previously recorded upon transfer from available for sale	(4)	0	(9)	0
Other			1	0
Other comprehensive income (loss)	(4)	(29)	(35)	(99)
Net of Tax
Net unrealized gain (loss)	0	48	51	166
Reclassification of net unrealized loss on securities transferred to held to maturity			142	0
Other reclassifications included in other revenue	0	0	(4)	(2)
Change in net unrealized gain (loss) on held to maturity securities:
Reclassification of net unrealized loss on securities transferred from available for sale			(142)	0
Amortization of amounts previously recorded upon transfer from available for sale	6	0	12	0
Other			(2)	1
Other comprehensive income (loss), net of tax	$ 6	$ 48	$ 57	$ 165