Equity - AOCI Changes Net of Tax Table (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Net of Tax Beginning of Period	$ (96)
Other Comprehensive Income (Loss)	39	$ 3	$ 44
Accumulated Other Comprehensive Income (Loss), Net of Tax End of Period	(57)	(96)
Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member]
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Net of Tax Beginning of Period	(96)	(99)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	5	(13)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	34	16
Other Comprehensive Income (Loss)	39	3
Accumulated Other Comprehensive Income (Loss), Net of Tax End of Period	$ (57)	$ (96)	$ (99)