Derivative and Hedging Activities - Cash Flow Hedges Components of AOCI Table (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Net of Tax Period Start	$ (96)
Other Comprehensive Income (Loss), Net Change in Fair Value, Net of Tax	4	$ (4)
Other Comprehensive Income (Loss), Losses Reclassified to Income, Net of Tax	10	4
Accumulated Other Comprehensive Income (Loss), Net of Tax Period End	(82)
Cash Flow Hedging [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Before Tax, Period Start	(153)	(160)
Accumulated Other Comprehensive Income (Loss), Net of Tax Period Start	(96)	(99)
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax	4	(7)
Other Comprehensive Income (Loss), Losses Reclassified to Income, Before Tax	10	11
Other Comprehensive Income (Loss), Losses Reclassified to Income, Net of Tax	10	4
Accumulated Other Comprehensive Income (Loss), Before Tax, Period End	(139)	(156)
Accumulated Other Comprehensive Income (Loss), Net of Tax Period End	$ (82)	$ (99)