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Derivative Instruments (Textuals) (Details) (USD $)
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3 Months Ended | 12 Months Ended | 3 Months Ended | |||||||||||||||
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Mar. 31, 2011
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Dec. 31, 2012
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Dec. 31, 2011
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Dec. 31, 2010
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Dec. 31, 2012
Interest Rate Swap [Member]
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Dec. 31, 2011
Interest Rate Swap [Member]
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Dec. 31, 2010
Interest Rate Swap [Member]
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Mar. 31, 2012
Interest Rate Swap [Member]
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| Derivatives, Fair Value [Line Items] | ||||||||||||||||||
| Gain (Loss) on Sale of Derivatives | $ 230,000,000 | [1] | $ (50,000,000) | [1] | $ 83,000,000 | [1] | $ (157,000,000) | [1] | $ (193,000,000) | [1] | $ (31,000,000) | [1] | ||||||
| Derivative Instruments (Textuals) [Abstract] | ||||||||||||||||||
| Maximum length of time hedging using interest rate derivative instruments | 11 years | |||||||||||||||||
| Derivative, Net Liability Position, Aggregate Fair Value | 5,000,000 | |||||||||||||||||
| Collateral Already Posted, Aggregate Fair Value | 1,000,000 | |||||||||||||||||
| Additional Collateral, Aggregate Fair Value | 1,000,000 | |||||||||||||||||
| Early Repayment of Senior Debt | 1,200,000,000 | 3,500,000,000 | ||||||||||||||||
| Notional Amount Interest Rate Derivative Underlying Debt Repaid During Period | 1,000,000,000 | |||||||||||||||||
| Gain (Loss) on Discontinuation of Cash Flow Hedge Due to Forecasted Transaction Probable of Not Occurring, Net | 91,000,000 | 91,000,000 | 206,000,000 | |||||||||||||||
| Unrealized losses associated with interest rate swap breakage costs | 32,000,000 | |||||||||||||||||
| Cumulative cash flow hedge losses remaining in AOCI | 242,000,000 | 172,000,000 | ||||||||||||||||
| Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months | 41,000,000 | |||||||||||||||||
| Losses from interest rate contracts reclassified from OCI into earnings | 15,000,000 | |||||||||||||||||
| Notional Amount Interest Rate Derivative Underlying Debt Repaid | 4,100,000,000 | 3,300,000,000 | ||||||||||||||||
| Losses from reclassification of interest rate contracts due to settlement | 17,000,000 | |||||||||||||||||
| Gain (Loss) on Interest Rate Derivative Instruments Not Designated as Hedging Instruments | (14,000,000) | (145,000,000) | (223,000,000) | 156,000,000 | ||||||||||||||
| Gain Loss On Interest Rate Derivative Instruments Not Designated As Hedging Instruments, Unrealized | 14,000,000 | |||||||||||||||||
| Gain Loss On Interest Rate Derivative Instruments Not Designated As Hedging Instruments, Realized | 142,000,000 | |||||||||||||||||
| Unrealized Gain (Loss) on Derivatives | 72,000,000 | [2] | 30,000,000 | [2] | (56,000,000) | [2] | 154,000,000 | [2] | 55,000,000 | [2] | (199,000,000) | [2] | ||||||
| Interest rate swaps included in interest expense | $ (11,000,000) | $ (7,000,000) | $ 7,000,000 | |||||||||||||||
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