Accumulated Other Comprehensive Income (Accumulated Other Comprehensive Income Balances) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Accumulated Other Comprehensive Income [Line Items]
Beginning Balance	$ (134)	[1]	$ 165		$ 9
Other net changes	(29)		(299)		156
Ending Balance	(163)		(134)	[1]	165
Net Unrealized Gain (Loss) On Available For Sale Securities [Member]
Accumulated Other Comprehensive Income [Line Items]
Other net changes	(30)		$ (299)		$ 156
Other [Member]
Accumulated Other Comprehensive Income [Line Items]
Other net changes	$ 1

[1] Adjusted for the retrospective adoption of ASU 2015-03. See New Accounting Standards in Note 2 for additional information.