Fair Value (Quantitative Information) (Details) (USD $)	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Assets Liabilities Value	$ (69,000,000)	$ (396,000,000)	$ (122,000,000)	$ (148,000,000)
Interest Rate Derivatives
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Assets Liabilities Value	(72,000,000)	(412,000,000)	(124,000,000)	(128,000,000)
Interest Rate Derivatives | Minimum
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Subsidiaries' credit risk	2.15%
Interest Rate Derivatives | Maximum
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Subsidiaries' credit risk	9.03%
Interest Rate Derivatives | Weighted Average
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Subsidiaries' credit risk	4.35%
Foreign Currency Embedded Derivative Argentine Peso [Member]
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Assets Liabilities Value	70,000,000
Foreign Currency Embedded Derivative Argentine Peso [Member] | Minimum
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Argentine Peso to U.S. Dollar currency exchange rate after 2 years	14.4
Foreign Currency Embedded Derivative Argentine Peso [Member] | Maximum
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Argentine Peso to U.S. Dollar currency exchange rate after 2 years	21.2
Foreign Currency Embedded Derivative Argentine Peso [Member] | Weighted Average
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Argentine Peso to U.S. Dollar currency exchange rate after 2 years	17.7
Commodity And Other Derivative Other [Member]
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Assets Liabilities Value	(2,000,000)
Commodity And Other Embedded Derivative Aluminum [Member]
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Assets Liabilities Value	(65,000,000)
Commodity And Other Embedded Derivative Aluminum [Member] | Minimum
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Market Price of Power for Customer in Cameroon (per KWh)	0.06
Commodity And Other Embedded Derivative Aluminum [Member] | Maximum
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Market Price of Power for Customer in Cameroon (per KWh)	0.14
Commodity And Other Embedded Derivative Aluminum [Member] | Weighted Average
Fair Value Derivative Assets Liabilities Measured On Recurring Basis Unobservable Inputs [Abstract]
Market Price of Power for Customer in Cameroon (per KWh)	$ 0.12