Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 94	$ 72	$ (2)	$ 69	$ 203	$ 116	$ 29	$ 89	$ 233	$ 437	$ 217
Other comprehensive income:
Reclassification of cash flow hedge losses into earnings									1	2	4
Total other comprehensive income									1	2	4
Total comprehensive income									234	439	221
Total comprehensive income attributable to noncontrolling interests									(5)	(14)	(17)
Total comprehensive income attributable to partners									$ 229	$ 425	$ 204