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Fair Value of Financial Instruments (Schedule of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis) (Details) (USD $)
In Millions, unless otherwise specified |
Mar. 31, 2013
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Dec. 31, 2012
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| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||||||||
| Financial investments, at fair value | $ 218 | [1] | $ 223 | [1] | ||||
| Default fund investments | 191 | [2] | 175 | [2] | ||||
| Total | 409 | 398 | ||||||
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Level 1 [Member]
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| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||||||||
| Financial investments, at fair value | 218 | [1] | 223 | [1] | ||||
| Default fund investments | 73 | [2] | 175 | [2] | ||||
| Total | 291 | 398 | ||||||
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Level 2 [Member]
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| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||||||||
| Default fund investments | 118 | [2] | ||||||
| Total | $ 118 | |||||||
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