Discontinued Operations and Held-For-Sale Businesses (Narrative) (Details) (USD $)	12 Months Ended			7 Months Ended	0 Months Ended		1 Months Ended	0 Months Ended	1 Months Ended		12 Months Ended	1 Months Ended	3 Months Ended
	Dec. 31, 2014 MW	Dec. 31, 2013	Dec. 31, 2012	Mar. 31, 2014	Feb. 24, 2014	Jan. 30, 2014	Nov. 30, 2013 MW project	Apr. 29, 2013 business	Apr. 30, 2012	Dec. 31, 2012	Dec. 31, 2010	Jun. 30, 2014 business	Jun. 30, 2014 business	Sep. 30, 2013	Oct. 31, 2013 MW	Mar. 31, 2011 MW plant
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Asset impairment expense	$ 383,000,000	$ 661,000,000	$ 1,940,000,000
Net gain (loss) from disposal and impairments of discontinued operations	(56,000,000)	(152,000,000)	16,000,000
Production Capacity (MW)	2,072
Cameroon businesses
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Summary of Investments, Other than Investments in Related Parties, Carrying Amount												435,000,000	435,000,000
Asset impairment expense				101,000,000
Fair value less costs to sell												334,000,000	334,000,000
Sonel
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Divestiture of ownership in subsidiary percent														56.00%
Kribi
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Divestiture of ownership in subsidiary percent														56.00%
Dibamba
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Divestiture of ownership in subsidiary percent														56.00%
Saurashtra
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from divestiture of business					8,000,000
Production Capacity (MW)															39
U.S. wind projects
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Divestiture of ownership in subsidiary percent							100.00%
Proceeds from divestiture of business						27,000,000
Asset impairment expense							47,000,000
Fair value less costs to sell							30,000,000
Number of wind projects							3
Production Capacity (MW)							234
Asset impairment charges attributable to noncontrolling interest							7,000,000
Assets carrying amount							77,000,000
Deferred proceeds from divestiture of business						3,000,000
Poland wind projects
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from divestiture of business							7,000,000
Asset impairment expense							65,000,000
Net gain (loss) from disposal and impairments of discontinued operations							(2,000,000)
Number of wind projects							10
Kiev and Rivne
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from divestiture of business								113,000,000
Asset impairment expense								38,000,000
Number of power distribution businesses sold								2
Kiev
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Divestiture of ownership in subsidiary percent								89.10%
Customers served								881,000
Rivne
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Divestiture of ownership in subsidiary percent								84.60%
Customers served								412,000
Tisza I I Subsidiary
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Divestiture of ownership in subsidiary percent			100.00%							100.00%
Proceeds from divestiture of business			14,000,000
Net gain (loss) from disposal and impairments of discontinued operations			87,000,000
Production Capacity (MW)			900							900
Gain (loss) on disposal of discontinued operation from cumulative translation losses			(73,000,000)
Red Oak and Ironwood
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Divestiture of ownership in subsidiary percent									100.00%
Proceeds from divestiture of business									228,000,000
Net gain (loss) from disposal and impairments of discontinued operations									73,000,000
Red Oak
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Production Capacity (MW)									832
Ironwood
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Production Capacity (MW)									710
Eastern Energy Subsidiary
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Asset impairment expense											827,000,000
Net gain (loss) from disposal and impairments of discontinued operations										30,000,000
Production Capacity (MW)																1,169
Number of Power Plants Held-for-sale																4
Minimum | Poland wind projects
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Divestiture of ownership in subsidiary percent							61.00%
Maximum | Poland wind projects
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Divestiture of ownership in subsidiary percent							89.00%
Armenia Mountain
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Production Capacity (MW)							101
Sale agreement, buyer option to purchase ownership percent							100.00%
Sale Agreement, Buyer Option To Purchase Ownership Interest, Sales Price							75,000,000
Cameroon businesses
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of Equity Interests Sold												3	3
Disposal Group, Including Discontinued Operation, Consideration												200,000,000	200,000,000
Proceeds from divestiture of business												156,000,000
Letter of Credit Related to Sale Agreement	40,000,000
Net gain (loss) from disposal and impairments of discontinued operations													(7,000,000)
Cameroon businesses | Noncurrent Asset
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Non-contingent Consideration, Fair Value, Amount to be Received												44,000,000	44,000,000
Summary of Investments, Other than Investments in Related Parties, Carrying Amount	$ 44,000,000