Stockholders' Equity (Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Accumulated Other Comprehensive Income [Line Items]
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax	$ (4)	$ 2	$ 0	$ 2
Unrealized gain (loss), net of taxes of $0	0	0	0	0
Unrealized gain (loss), net of taxes of $0	5	0	(3)	0
Unrealized gain (loss), net of taxes of $0	(5)	3	1	4
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance			(1)	4
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Unrealized gain (loss), net of tax			(2)	4
Total other comprehensive income (loss)	(2)	3	(2)	4
Ending Balance	(3)	8	(3)	8
Tax effect on amounts reclassified from accumulated other comprehensive income			0	2
Unrealized Gain on Available-for-Sale Securities
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance			0	4
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Ending Balance	1	$ 8	1	$ 8
Unrealized Loss on Cash Flow Hedges
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance			(1)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [Abstract]
Ending Balance	$ (4)		$ (4)