Segment Reporting (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013		Jun. 30, 2014	Jun. 30, 2013		Dec. 31, 2013
Segment Reporting
Operating revenues	$ 134	$ 82	[1]	$ 274	$ 135	[1]
Cost of operations	45	32		105	61
Depreciation and amortization	36	10	[1]	60	20	[1]
General and administrative — affiliate	2	2	[1]	4	4	[1]
Operating Income	51	38	[1]	105	50	[1]
Equity in earnings of unconsolidated affiliates	14	2	[1]	15	6	[1]
Interest Expense	(29)	(6)	[1]	(56)	(11)	[1]
Other Income		1		1	1
Income/(loss) before income taxes	36	35	[1]	65	46	[1]
Income Tax Expense (Benefit)	2	0	[1]	5	0	[1]
Net income/(loss)	34	35	[1]	60	46	[1]
Total assets	3,236			3,236			3,238	[1]
Conventional Generation
Segment Reporting
Operating revenues	61	20		117	20
Cost of operations	12	3		22	3
Depreciation and amortization	24	2		36	2
Operating Income	25	15		59	15
Equity in earnings of unconsolidated affiliates	4	3		7	7
Interest Expense	(11)	(3)		(22)	(3)
Other Income		1		0	1
Income/(loss) before income taxes	18	16		44	20
Net income/(loss)	18	16		44	20
Total assets	1,535			1,535
Renewables
Segment Reporting
Operating revenues	30	26		49	42
Cost of operations	3	2		7	5
Depreciation and amortization	7	5		15	11
Operating Income	20	19		27	26
Equity in earnings of unconsolidated affiliates	10	(1)		8	(1)
Interest Expense	(11)	(1)		(22)	(4)
Other Income		0		1	0
Income/(loss) before income taxes	19	17		14	21
Net income/(loss)	19	17		14	21
Total assets	905			905
Thermal
Segment Reporting
Operating revenues	43	36		108	73
Cost of operations	30	27		76	53
Depreciation and amortization	5	3		9	7
Operating Income	8	6		23	13
Equity in earnings of unconsolidated affiliates	0	0		0	0
Interest Expense	(2)	(2)		(4)	(4)
Other Income		0		0	0
Income/(loss) before income taxes	6	4		19	9
Net income/(loss)	6	4		19	9
Total assets	362			362
Corporate
Segment Reporting
Operating revenues	0	0		0	0
Cost of operations	0	0		0	0
Depreciation and amortization	0	0		0	0
Operating Income	(2)	(2)		(4)	(4)
Equity in earnings of unconsolidated affiliates	0	0		0	0
Interest Expense	(5)	0		(8)	0
Other Income		0		0	0
Income/(loss) before income taxes	(7)	(2)		(12)	(4)
Net income/(loss)	(9)	(2)		(17)	(4)
Total assets	434			434
Affiliate
Segment Reporting
General and administrative — affiliate	2	2		4	4
Affiliate | Conventional Generation
Segment Reporting
General and administrative — affiliate	0	0		0	0
Affiliate | Renewables
Segment Reporting
General and administrative — affiliate	0	0		0	0
Affiliate | Thermal
Segment Reporting
General and administrative — affiliate	0	0		0	0
Affiliate | Corporate
Segment Reporting
General and administrative — affiliate	$ 2	$ 2		$ 4	$ 4

[1] Retrospectively adjusted as discussed in Note 1, Nature of Business.