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Derivative Instruments - Summary of Notional Amounts of AFS's Trading Derivative Products (Detail) (AFS [Member], USD $) In Thousands, unless otherwise specified | Sep. 30, 2012 | Dec. 31, 2011
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Interest Rate Swaps [Member] |  |
Schedule Of Notional Amounts Of Parents Financial Services Trading Derivative Products [Line Items] |  |
Derivative products, Notional Amount | $ 968,168 | $ 1,370,995
Interest Rate Swaps Pay Fixed Receive Variable [Member] |  |
Schedule Of Notional Amounts Of Parents Financial Services Trading Derivative Products [Line Items] |  |
Derivative products, Notional Amount | 1,745,806 | 3,798,305
Interest Rate Swaps Basis Swaps [Member] |  |
Schedule Of Notional Amounts Of Parents Financial Services Trading Derivative Products [Line Items] |  |
Derivative products, Notional Amount | 161,690 | 175,835
Currency Swaps [Member] |  |
Schedule Of Notional Amounts Of Parents Financial Services Trading Derivative Products [Line Items] |  |
Derivative products, Notional Amount |  | 13,559
Future Contracts [Member] |  |
Schedule Of Notional Amounts Of Parents Financial Services Trading Derivative Products [Line Items] |  |
Derivative products, Notional Amount | 258,000 | 53,500
Other Contracts [Member] |  |
Schedule Of Notional Amounts Of Parents Financial Services Trading Derivative Products [Line Items] |  |
Derivative products, Notional Amount | $ 75,651 | $ 118,930

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- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
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