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
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