Accumulated Other Comprehensive Income (Accumulated Other Comprehensive Income Balances) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income
Beginning Balance	$ (163)	$ (134)	$ 165
Other net changes	11	(29)	(299)
Ending Balance	(152)	(163)	(134)
Net unrealized gain (loss) on available for sale securities [Member]
Accumulated Other Comprehensive Income
Other net changes	6	(30)	$ (299)
Other [Member]
Accumulated Other Comprehensive Income
Other net changes	(7)	$ 1
Reclassification of 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	(8)
Reclassification of 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