Accumulated Other Comprehensive Income (Accumulated Other Comprehensive Income Balances) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income
Beginning Balance			$ (152)	$ (163)
Other net changes	$ (26)	$ 6	(119)	57
Ending Balance	$ (304)	$ (106)	(304)	(106)
Net unrealized gain (loss) on available for sale securities [Member]
Accumulated Other Comprehensive Income
Other net changes			(139)	51
Reclassification of net unrealized loss on securities transferred to held to maturity [Member]
Accumulated Other Comprehensive Income
Other net changes				142
Other reclassifications in other revenue, available for sale securities [Member]
Accumulated Other Comprehensive Income
Other net changes				(4)
Reclassification of net unrealized loss on securities transferred from available for sale [Member]
Accumulated Other Comprehensive Income
Other net changes				(142)
Amortization of amounts previously recorded upon transfer to held to maturity from available for sale [Member]
Accumulated Other Comprehensive Income
Other net changes			20	12
Other [Member]
Accumulated Other Comprehensive Income
Other net changes				$ (2)
Adoption of accounting standards [Member] | ASU 2018-02 [Member]
Accumulated Other Comprehensive Income
Other net changes			$ (33)