Derivative and Hedging Activities - Cash Flow Hedges Components of AOCI Table (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Net of Tax Period Start			$ (143)
Unrealized gains (losses) on derivative instruments, net of income tax expense (benefit) of $5, $0, $4 and $3	$ 7	$ 0	6	$ 3
Reclassification of (gains) losses on settled derivative instruments, net of income tax expense (benefit) of $2, $2, $11 and $12	5	3	18	13
Accumulated Other Comprehensive Income (Loss), Net of Tax Period End	(119)		(119)
Cash Flow Hedging [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Before Tax, Period End	(211)	(243)	(231)	(269)
Accumulated Other Comprehensive Income (Loss), Net of Tax Period Start	(131)	(154)	(143)	(167)
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax	12	0	10	6
Unrealized gains (losses) on derivative instruments, net of income tax expense (benefit) of $5, $0, $4 and $3			6	3
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax	7	5	29	25
Reclassification of (gains) losses on settled derivative instruments, net of income tax expense (benefit) of $2, $2, $11 and $12	5	3	18	13
Accumulated Other Comprehensive Income (Loss), Before Tax, Period End	(192)	(238)	(192)	(238)
Accumulated Other Comprehensive Income (Loss), Net of Tax Period End	$ (119)	$ (151)	$ (119)	$ (151)