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Fair Value Of Financial Instruments (Narrative) (Detail) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2014 | Sep. 30, 2013 | Sep. 30, 2014 | Sep. 30, 2013 | Dec. 31, 2013
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |  |  |  |
Percentage of insured credit derivatives, value under Direct Price Model and Dual-Default Model | 6.00% |  | 6.00% |  |
Percentage of sector-specific transactions valued using BET model | 6.00% |  | 6.00% |  |
Percentage of transactions valued using corporate spreads used | 44.00% |  | 44.00% |  |
Percentage of transactions valued using spread benchmarked from most relevant spread source | 50.00% |  | 50.00% |  |
Percentage of transactions valued using WARF-sourced and/or ratings sourced credit spreads | 76.00% |  | 76.00% |  |
Net insured derivative liability | $ 284 |  | $ 284 |  | $ 1,200
Impact of including the nonperformance risk in valuation of pre-tax net insured derivative liability | 94 |  | 94 |  | 394
Percentage of level 3 assets at fair value in total assets measured at fair value value | 22.00% |  | 22.00% |  | 22.00%
Percentage of level 3 liabilities at fair value in total liabilities measured at fair value | 41.00% |  | 41.00% |  | 61.00%
Transfers into Level 3 | 55 | 41 | 238 | 199 |
Transfers out of Level 3 | 1 | 34 | 83 | 132 |
Transfers into Level 2 | 1 | 34 | 83 | 132 |
Transfers out of Level 2 | 55 | 41 | 238 | 199 |
Transfers into or out of Level 1 | $ 0 | $ 0 | $ 0 | $ 0 |
B E T Valuation Model [Member] |  |  |  |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |  |  |  |
Percentage of insured credit derivatives, fair value using the BET model | 94.00% |  | 94.00% |  |

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