Segment and Related Information - Income Statement Data (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues from external customers		$ 1,419	$ 1,601	$ 3,430	$ 1,653
Operating income (loss)		(246)	189	(34)	126
Operating Segments | East
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues from external customers	[1]	1,325	1,601	3,305	1,653
Operating income (loss)		(230)	242	132	307
Operating Segments | West
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues from external customers	[1]	94	0	125	0
Operating income (loss)		24	0	18	0
Other
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating income (loss)		$ (40)	$ (53)	$ (184)	$ (181)

[1] Includes unrealized gains and losses from derivatives. See Note 14 for additional information.