Fair Value (Details) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Fair Value Disclosures Details [Abstract]
An input assumption is considered significant if it affects the fair value by at least 10%.	10.00%
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Available-for-sale securities	$ 1,717,000,000		$ 1,340,000,000
Trading securities	12,000,000		12,000,000
Derivatives	109,000,000		120,000,000
Total assets	1,838,000,000		1,472,000,000
Derivatives	648,000,000		690,000,000
Total liabilities	648,000,000		690,000,000
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Asset Impairment Charges	11,000,000	0
Other non-operating expense	49,000,000	0
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	(148,000,000)	49,000,000
Included in earnings	5,000,000	11,000,000
Included in other comprehensive income	15,000,000	(12,000,000)
Included in regulatory (assets) liabilities	0	(1,000,000)
Settlements	8,000,000	2,000,000
Transfers of assets (liabilities) into Level 3	(28,000,000)	(4,000,000)
Transfers of (assets) liabilities out of Level 3	26,000,000
Balance at end of period	(122,000,000)	45,000,000
Total gains/(losses) for the period included in earnings attributable to the change in unrealized gains/(losses) relating to assets and liabilities held at the end of the period	6,000,000	10,000,000
Debt securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	0	42,000,000
Settlements	0	(2,000,000)
Balance at end of period	0	40,000,000
Total gains/(losses) for the period included in earnings attributable to the change in unrealized gains/losses relating to assets held at the end of the period	0	0
Interest Rate Derivatives
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	(128,000,000)	(1,000,000)
Included in earnings	(1,000,000)	0
Included in other comprehensive income	1,000,000	(4,000,000)
Included in regulatory (assets) liabilities	0	0
Settlements	6,000,000	0
Transfers of assets (liabilities) into Level 3	(28,000,000)	(2,000,000)
Transfers of (assets) liabilities out of Level 3	26,000,000
Balance at end of period	(124,000,000)	(7,000,000)
Total gains/(losses) for the period included in earnings attributable to the change in unrealized gains/(losses) relating to assets and liabilities held at the end of the period	0	0
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Own credit risk (minimum)	3.30%
Own credit risk (maximum)	4.10%
Own credit risk (weighted average)	3.50%
Cross Currency Swaps
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	(18,000,000)	10,000,000
Included in earnings	0	2,000,000
Included in other comprehensive income	14,000,000	(8,000,000)
Included in regulatory (assets) liabilities	0	0
Settlements	4,000,000	1,000,000
Transfers of assets (liabilities) into Level 3	0	0
Transfers of (assets) liabilities out of Level 3	0
Balance at end of period	0	5,000,000
Total gains/(losses) for the period included in earnings attributable to the change in unrealized gains/(losses) relating to assets and liabilities held at the end of the period	0	2,000,000
Foreign Currency
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	51,000,000	22,000,000
Included in earnings	(2,000,000)	1,000,000
Included in other comprehensive income	0	0
Included in regulatory (assets) liabilities	0	0
Settlements	(1,000,000)	1,000,000
Transfers of assets (liabilities) into Level 3	0	(1,000,000)
Transfers of (assets) liabilities out of Level 3	0
Balance at end of period	48,000,000	23,000,000
Total gains/(losses) for the period included in earnings attributable to the change in unrealized gains/(losses) relating to assets and liabilities held at the end of the period	(3,000,000)	0
Commodity & Other
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	(53,000,000)	18,000,000
Included in earnings	8,000,000	8,000,000
Included in other comprehensive income	0	0
Included in regulatory (assets) liabilities	0	(1,000,000)
Settlements	(1,000,000)	0
Transfers of assets (liabilities) into Level 3	0	(1,000,000)
Transfers of (assets) liabilities out of Level 3	0
Balance at end of period	(46,000,000)	24,000,000
Total gains/(losses) for the period included in earnings attributable to the change in unrealized gains/(losses) relating to assets and liabilities held at the end of the period	9,000,000	8,000,000
Foreign currency: Embedded derivative - Argentina Peso
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance at end of period	48,000,000
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Embedded derivative - Argentine Peso	6.13
Foreign currency: Other
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance at end of period	0
Commodity & other: Embedded derivative - Philippine Peso
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance at end of period	10,000,000
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
U.S. Producer Price Index after 5 years (where base year of 2005 = 100), Minimum	143
U.S. Producer Price Index after 5 years (where base year of 2005 = 100), Maximum	174
U.S. Producer Price Index after 5 years (where base year of 2005 = 100), Weighted Average	157
Commodity & other: Other
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance at end of period	(2,000,000)
Commodity & other: Embedded derivative - Aluminum
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance at end of period	(54,000,000)
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Market Price of Power for Customer in Cameroon (per MWh), Minimum	0.06
Market Price of Power for Customer in Cameroon (per MWh), Maximum	0.18
Market Price Of Power For Customer In Cameroon Weighted Average	0.13
Nonrecurring | Long Lived Assets Held And Used [Member] | Kelanitissa [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Asset Impairment Charges	5,000,000
Nonrecurring | Equity Method Affiliate [Member] | Other Subsidiary [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Other non-operating expense	49,000,000
Level 1
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Available-for-sale securities	2,000,000		1,000,000
Trading securities	12,000,000		12,000,000
Derivatives	2,000,000		2,000,000
Total assets	16,000,000		15,000,000
Derivatives	0		0
Total liabilities	0		0
Level 2
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Available-for-sale securities	1,715,000,000		1,339,000,000
Trading securities	0		0
Derivatives	41,000,000		52,000,000
Total assets	1,756,000,000		1,391,000,000
Derivatives	460,000,000		476,000,000
Total liabilities	460,000,000		476,000,000
Level 3
Fair Value Assets And Liabilities Measured On Recurring Basis Abstract
Available-for-sale securities	0		0
Trading securities	0		0
Derivatives	66,000,000		66,000,000
Total assets	66,000,000		66,000,000
Derivatives	188,000,000		214,000,000
Total liabilities	188,000,000		214,000,000
Carrying Amount
Financial Instruments Not Measured At Fair Value In the Condensed Consolidated Balance Sheets [Abstract]
Long-term receivables	408,000,000		386,000,000
Non-recourse debt	16,035,000,000		15,535,000,000
Recourse debt	6,200,000,000		6,485,000,000
Carrying Amount | Nonrecurring | Long Lived Assets Held And Used [Member] | Kelanitissa [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Carrying Amount, Nonrecurring	22,000,000
Carrying Amount | Nonrecurring | Equity Method Affiliate [Member] | Other Subsidiary [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Carrying Amount, Nonrecurring	204,000,000
Fair Value
Financial Instruments Not Measured At Fair Value In the Condensed Consolidated Balance Sheets [Abstract]
Long-term receivables	454,000,000		401,000,000
Non-recourse debt	16,369,000,000		15,862,000,000
Recourse debt	6,809,000,000		6,640,000,000
Fair Value | Level 1
Financial Instruments Not Measured At Fair Value In the Condensed Consolidated Balance Sheets [Abstract]
Long-term receivables	0
Non-recourse debt	0
Recourse debt	0
Fair Value | Level 1 | Nonrecurring | Long Lived Assets Held And Used [Member] | Kelanitissa [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	0
Fair Value | Level 1 | Nonrecurring | Equity Method Affiliate [Member] | Other Subsidiary [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	0
Fair Value | Level 2
Financial Instruments Not Measured At Fair Value In the Condensed Consolidated Balance Sheets [Abstract]
Long-term receivables	0
Non-recourse debt	15,339,000,000
Recourse debt	6,809,000,000
Fair Value | Level 2 | Nonrecurring | Long Lived Assets Held And Used [Member] | Kelanitissa [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	0
Fair Value | Level 2 | Nonrecurring | Equity Method Affiliate [Member] | Other Subsidiary [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	155,000,000
Fair Value | Level 3
Financial Instruments Not Measured At Fair Value In the Condensed Consolidated Balance Sheets [Abstract]
Long-term receivables	454,000,000
Non-recourse debt	1,030,000,000
Recourse debt	0
Fair Value | Level 3 | Nonrecurring | Long Lived Assets Held And Used [Member] | Kelanitissa [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	17,000,000
Fair Value | Level 3 | Nonrecurring | Equity Method Affiliate [Member] | Other Subsidiary [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Fair Value, Nonrecurring	$ 0