Fair Value (Nonrecurring Measurements) (Details) - USD ($)		1 Months Ended	2 Months Ended	3 Months Ended				5 Months Ended	6 Months Ended		8 Months Ended	9 Months Ended
		Feb. 09, 2015	Feb. 28, 2014	Sep. 30, 2015	Mar. 31, 2015	Sep. 30, 2014	Mar. 31, 2014	Jun. 06, 2014	Jun. 30, 2015	Jun. 30, 2014	Aug. 28, 2015	Sep. 30, 2015	Sep. 30, 2014	Sep. 25, 2014
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Other Nonoperating Expense				$ 0		$ 16,000,000						$ 0	$ 60,000,000
Impairment expenses												276,000,000	304,000,000
Goodwill impairment expense				0		0						0	154,000,000
East Bend DPL [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring							$ 2,000,000
Ebute [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring						36,000,000				$ 47,000,000			36,000,000
UK Wind (Newfield) [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring						0							0
DPLER [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Goodwill impairment expense							136,000,000
Buffalo Gap [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Goodwill impairment expense							18,000,000
Kilroot [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring				78,000,000								78,000,000
buffalo gap III [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring				116,000,000								116,000,000
UK Wind Development Projects [Domain]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring									$ 1,000,000
Long Lived Assets Held And Used [Member] | East Bend DPL [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Impairment expenses	[1]						12,000,000
Long Lived Assets Held And Used [Member] | Ebute [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Impairment expenses	[1]									52,000,000			15,000,000
Long Lived Assets Held And Used [Member] | UK Wind (Newfield) [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Impairment expenses	[1]							$ 11,000,000
Long Lived Assets Held And Used [Member] | Kilroot [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Other Nonoperating Expense	[1]										$ 113,000,000
Long Lived Assets Held And Used [Member] | buffalo gap III [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Other Nonoperating Expense	[1]											118,000,000
Long Lived Assets Held And Used [Member] | Other Affiliates [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Other Nonoperating Expense	[1]				$ 8,000,000
Long Lived Assets Held And Used [Member] | UK Wind Development Projects [Domain]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Other Nonoperating Expense	[1]								37,000,000
Long Lived Assets Held And Used [Member] | Fair Value [Member] | East Bend DPL [Member] | Level 1 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[1]						0
Long Lived Assets Held And Used [Member] | Fair Value [Member] | East Bend DPL [Member] | Level 2 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[1]						2,000,000
Long Lived Assets Held And Used [Member] | Fair Value [Member] | East Bend DPL [Member] | Level 3 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[1]						0
Long Lived Assets Held And Used [Member] | Fair Value [Member] | Ebute [Member] | Level 1 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[1]					0				0			0
Long Lived Assets Held And Used [Member] | Fair Value [Member] | Ebute [Member] | Level 2 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[1]					0				0			0
Long Lived Assets Held And Used [Member] | Fair Value [Member] | Ebute [Member] | Level 3 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[1]					36,000,000				47,000,000			36,000,000
Long Lived Assets Held And Used [Member] | Fair Value [Member] | UK Wind (Newfield) [Member] | Level 1 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[1]							0
Long Lived Assets Held And Used [Member] | Fair Value [Member] | UK Wind (Newfield) [Member] | Level 2 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[1]							0
Long Lived Assets Held And Used [Member] | Fair Value [Member] | UK Wind (Newfield) [Member] | Level 3 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[1]							0
Long Lived Assets Held And Used [Member] | Fair Value [Member] | Kilroot [Member] | Level 1 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[1]										0
Long Lived Assets Held And Used [Member] | Fair Value [Member] | Kilroot [Member] | Level 2 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[1]										0
Long Lived Assets Held And Used [Member] | Fair Value [Member] | buffalo gap III [Member] | Level 1 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[1]			0								0
Long Lived Assets Held And Used [Member] | Fair Value [Member] | buffalo gap III [Member] | Level 2 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[1]			0								0
Long Lived Assets Held And Used [Member] | Fair Value [Member] | Other Affiliates [Member] | Level 1 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[1]				0
Long Lived Assets Held And Used [Member] | Fair Value [Member] | Other Affiliates [Member] | Level 2 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[1]				21,000,000
Long Lived Assets Held And Used [Member] | Fair Value [Member] | Other Affiliates [Member] | Level 3 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[1]				0
Long Lived Assets Held And Used [Member] | Fair Value [Member] | UK Wind Development Projects [Domain] | Level 1 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[1]								0
Long Lived Assets Held And Used [Member] | Fair Value [Member] | UK Wind Development Projects [Domain] | Level 2 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[1]								1,000,000
Long Lived Assets Held And Used [Member] | Fair Value [Member] | UK Wind Development Projects [Domain] | Level 3 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[1]								0
Long Lived Assets Held And Used [Member] | Carrying Amount [Member] | East Bend DPL [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[1],[2]						14,000,000
Long Lived Assets Held And Used [Member] | Carrying Amount [Member] | Ebute [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[1],[2]					$ 51,000,000				99,000,000			$ 51,000,000
Long Lived Assets Held And Used [Member] | Carrying Amount [Member] | UK Wind (Newfield) [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[1],[2]							$ 11,000,000
Long Lived Assets Held And Used [Member] | Carrying Amount [Member] | Kilroot [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[1],[2]										191,000,000
Long Lived Assets Held And Used [Member] | Carrying Amount [Member] | buffalo gap III [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[1],[2]			234,000,000								234,000,000
Long Lived Assets Held And Used [Member] | Carrying Amount [Member] | Other Affiliates [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[1],[2]				$ 29,000,000
Long Lived Assets Held And Used [Member] | Carrying Amount [Member] | UK Wind Development Projects [Domain]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[1],[2]								$ 38,000,000
Goodwill [Member] | DPLER [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Goodwill impairment expense	[3]		$ 136,000,000
Goodwill [Member] | Buffalo Gap [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Goodwill impairment expense	[3]						18,000,000
Goodwill [Member] | Fair Value [Member] | DPLER [Member] | Level 1 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[3]		0
Goodwill [Member] | Fair Value [Member] | DPLER [Member] | Level 2 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[3]		0
Goodwill [Member] | Fair Value [Member] | DPLER [Member] | Level 3 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[3]		0
Goodwill [Member] | Fair Value [Member] | Buffalo Gap [Member] | Level 1 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[3]						0
Goodwill [Member] | Fair Value [Member] | Buffalo Gap [Member] | Level 2 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[3]						0
Goodwill [Member] | Fair Value [Member] | Buffalo Gap [Member] | Level 3 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[3]						10,000,000
Goodwill [Member] | Carrying Amount [Member] | DPLER [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[2],[3]		$ 136,000,000
Goodwill [Member] | Carrying Amount [Member] | Buffalo Gap [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[2],[3]						28,000,000
Equity Method Investments [Member] | Silver Ridge Power [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Other Nonoperating Expense	[4]									42,000,000
Equity Method Investments [Member] | Entek [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Other Nonoperating Expense	[4]													$ 18,000,000
Equity Method Investments [Member] | Solar Spain [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Other Nonoperating Expense		$ 0
Equity Method Investments [Member] | Fair Value [Member] | Silver Ridge Power [Member] | Level 1 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[4]									0
Equity Method Investments [Member] | Fair Value [Member] | Silver Ridge Power [Member] | Level 2 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[4]									0
Equity Method Investments [Member] | Fair Value [Member] | Silver Ridge Power [Member] | Level 3 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[4]									273,000,000
Equity Method Investments [Member] | Fair Value [Member] | Entek [Member] | Level 1 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[4]													0
Equity Method Investments [Member] | Fair Value [Member] | Entek [Member] | Level 2 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[4]													125,000,000
Equity Method Investments [Member] | Fair Value [Member] | Entek [Member] | Level 3 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[4]													0
Equity Method Investments [Member] | Fair Value [Member] | Solar Spain [Member] | Level 1 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring		0
Equity Method Investments [Member] | Fair Value [Member] | Solar Spain [Member] | Level 2 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring		0
Equity Method Investments [Member] | Fair Value [Member] | Solar Spain [Member] | Level 3 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring		29,000,000		29,000,000								$ 29,000,000
Equity Method Investments [Member] | Carrying Amount [Member] | Silver Ridge Power [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[2],[4]									$ 315,000,000
Equity Method Investments [Member] | Carrying Amount [Member] | Entek [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[2],[4]													$ 143,000,000
Equity Method Investments [Member] | Carrying Amount [Member] | Solar Spain [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[2]	$ 29,000,000
Discontinued Operations, Held-for-sale or Disposed of by Sale [Member] | Cameroon [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Impairment expenses	[4]						38,000,000
Discontinued Operations, Held-for-sale or Disposed of by Sale [Member] | Fair Value [Member] | Cameroon [Member] | Level 1 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[4]						0
Discontinued Operations, Held-for-sale or Disposed of by Sale [Member] | Fair Value [Member] | Cameroon [Member] | Level 2 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[4]						334,000,000
Discontinued Operations, Held-for-sale or Disposed of by Sale [Member] | Fair Value [Member] | Cameroon [Member] | Level 3 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[4]						0
Discontinued Operations, Held-for-sale or Disposed of by Sale [Member] | Carrying Amount [Member] | Cameroon [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[2],[4]						$ 372,000,000
Income Approach Valuation Technique [Member] | Equity Method Investments [Member] | Weighted Average [Member] | Solar Spain [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Inputs, Long-term Revenue Growth Rate												0.00%
Fair Value Inputs, Long-term Pre-tax Operating Margin, Percent												24.00%
Fair Value Inputs, Discount Rate												12.00%
Income Approach Valuation Technique [Member] | Equity Method Investments [Member] | Maximum [Member] | Solar Spain [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Inputs, Long-term Revenue Growth Rate												0.00%
Fair Value Inputs, Long-term Pre-tax Operating Margin, Percent												56.00%
Fair Value Inputs, Discount Rate
Income Approach Valuation Technique [Member] | Equity Method Investments [Member] | Minimum [Member] | Solar Spain [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Inputs, Long-term Revenue Growth Rate												(3.00%)
Fair Value Inputs, Long-term Pre-tax Operating Margin, Percent												(13.00%)
Fair Value Inputs, Discount Rate
Long Lived Assets Held And Used [Member] | Fair Value [Member] | Kilroot [Member] | Level 3 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[1]										$ 78,000,000
Long Lived Assets Held And Used [Member] | Long Lived Assets Held And Used [Member] | Fair Value [Member] | buffalo gap III [Member] | Level 3 [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	[1]			$ 116,000,000								$ 116,000,000
Long Lived Assets Held And Used [Member] | Income Approach Valuation Technique [Member] | Weighted Average [Member] | Kilroot [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Inputs, Long-term Revenue Growth Rate												(7.00%)
Fair Value Inputs, Long-term Pre-tax Operating Margin, Percent												0.00%
Fair Value Inputs, Discount Rate												6.00%
Long Lived Assets Held And Used [Member] | Income Approach Valuation Technique [Member] | Weighted Average [Member] | buffalo gap III [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Inputs, Long-term Revenue Growth Rate												3.00%
Fair Value Inputs, Long-term Pre-tax Operating Margin, Percent												24.00%
Fair Value Inputs, Discount Rate												9.00%
Long Lived Assets Held And Used [Member] | Income Approach Valuation Technique [Member] | Maximum [Member] | Kilroot [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Inputs, Long-term Revenue Growth Rate												6.00%
Fair Value Inputs, Long-term Pre-tax Operating Margin, Percent												10.00%
Fair Value Inputs, Discount Rate
Long Lived Assets Held And Used [Member] | Income Approach Valuation Technique [Member] | Maximum [Member] | buffalo gap III [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Inputs, Long-term Revenue Growth Rate												19.00%
Fair Value Inputs, Long-term Pre-tax Operating Margin, Percent												58.00%
Long Lived Assets Held And Used [Member] | Income Approach Valuation Technique [Member] | Minimum [Member] | Kilroot [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Inputs, Long-term Revenue Growth Rate												(88.00%)
Fair Value Inputs, Long-term Pre-tax Operating Margin, Percent												(74.00%)
Fair Value Inputs, Discount Rate
Long Lived Assets Held And Used [Member] | Income Approach Valuation Technique [Member] | Minimum [Member] | buffalo gap III [Member]
Fair Value Assets Measured On Nonrecurring Basis Unobservable Inputs [Line Items]
Fair Value Inputs, Long-term Revenue Growth Rate												(2.00%)
Fair Value Inputs, Long-term Pre-tax Operating Margin, Percent												(282.00%)

[1] See Note 15—Asset Impairment Expense for further information.

[2] (1) Represents the carrying values at the dates of measurement, before fair value adjustment.

[3] See Note 14—Goodwill Impairment for further information.

[4] See Note 18—Discontinued Operations for further information.