Accumulated Other Comprehensive Income (Accumulated Other Comprehensive Income Balances) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Accumulated Other Comprehensive Income
Beginning Balance	$ (163)	$ (134)
Other net changes	31	14
Ending Balance	(132)	(120)
Net unrealized gain (loss) on available for sale securities [Member]
Accumulated Other Comprehensive Income
Other net changes	33	13
Other [Member]
Accumulated Other Comprehensive Income
Other net changes	(2)	$ 1
Reclassification of Securities Transferred to Held to Maturity [Member]
Accumulated Other Comprehensive Income
Other net changes	142
Other Reclassifications in Other Revenue [Member]
Accumulated Other Comprehensive Income
Other net changes	(1)
Reclassification of Securities Transferred to 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	$ 1