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Derivative Instruments (Textuals) (Details) (USD $) | 3 Months Ended | 12 Months Ended | 3 Months Ended
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Mar. 31, 2011 | Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2012 Interest Rate Swap [Member] | Dec. 31, 2011 Interest Rate Swap [Member] | Dec. 31, 2010 Interest Rate Swap [Member] | Mar. 31, 2012 Interest Rate Swap [Member]
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 |  |  |  |  |  |  |  |
[1] | Does not include the realized value associated with derivative instruments that settle through physical delivery.
[2] | In addition to changes in market value on derivatives not designated as hedges, changes in unrealized gain (loss) also includes de-designation of interest rate swap cash flow hedges and related reclassification from AOCI into earnings, hedge ineffectiveness and adjustments to reflect changes in credit default risk exposure.

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- Definition Gain Loss On Interest Rate Derivative Instruments Not Designated As Hedging Instruments, Unrealized + References No definition available. + Details
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- Definition Losses from interest rate contracts reclassified from OCI into earnings + References No definition available. + Details
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- Definition Losses from reclassification of interest rate contracts due to settlement + References No definition available. + Details
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- Definition Notional Amount Interest Rate Derivative Underlying Debt Repaid + References No definition available. + Details
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- Definition Unrealized losses associated with interest rate swap breakage costs + References No definition available. + Details
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- Definition The aggregate fair value of additional assets that would be required to be posted as collateral for derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4H -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624258-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 44D -Subparagraph c -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
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- Definition The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=7668309&loc=d3e80748-113994 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 45 -Subparagraph b(2) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
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- Definition The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 44D -Subparagraph c -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4H -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624258-113959 + Details
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- Definition The aggregate fair value amounts of derivative instruments that contain credit-risk-related contingent features that are in a net liability position at the end of the reporting period. For nonderivative instruments that are designated and qualify as hedging instruments, the fair value amounts are the carrying value of the nonderivative hedging instrument, including the adjustment for the foreign currency transaction gain (loss) on that instrument. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4H -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624258-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 44D -Subparagraph b -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
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- Definition The cash outflow for the extinguishment of long-term borrowing, with the highest claim on the assets of the entity in case of bankruptcy or liquidation, before its maturity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 18 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Financing Activities -URI http://asc.fasb.org/extlink&oid=6513228 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 15 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3291-108585 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 20 -Subparagraph b -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
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- Definition The amount of net gain (loss) reclassified into earnings in the period when cash flow hedge is discontinued because it is probable that the original forecasted transactions will not occur by the end of the original period or an additional two month time period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=7668309&loc=d3e80748-113994 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 45 -Subparagraph b(4) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
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- Definition Amount of gain (loss) included in earnings for the period from the increase (decrease) in fair value of interest rate derivatives not designated as hedging instruments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5618551-113959 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624171-113959 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 44 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
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- Definition The difference between the book value and the sale price of options, swaps, futures, forward contracts, and other derivative instruments. This element refers to the gain (loss) included in earnings. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.13(h)) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882 + Details
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- Definition Maximum period the entity is hedging its exposure to the variability in future cash flows for forecasted transactions, excluding those forecasted transactions related to the payment of variable interest on existing financial instruments, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=7668309&loc=d3e80748-113994 + Details
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- Definition The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585 + Details
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