Derivative Instruments (Detail) (USD $)	3 Months Ended		9 Months Ended				9 Months Ended	11 Months Ended	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010	Dec. 30, 2010	Sep. 30, 2011 Deposit Liability Contracts [Member]	Sep. 30, 2011 Deposit Liability Contracts [Member]	Sep. 30, 2011 Notes Payable and Debt [Member]	Sep. 30, 2010 Notes Payable and Debt [Member]	Sep. 30, 2011 Structured Finance [Member]	Dec. 31, 2010 Structured Finance [Member]	Sep. 30, 2011 Collateralized Debt Obligations [Member]
Cash Collateral for Borrowed Securities	$ 54,000,000		$ 54,000,000		$ 23,000,000
Gain on Settlement of Derivative Part of Fair Value Hedge								149,500,000		21,600,000
Interest Expense Reduction							7,500,000		9,200,000
Gain on Settlement of Derivative Part of Fair Value Hedge Remaining to be Amortized							142,000,000		12,500,000
Remaining Period for Gain on Settlement of Derivative Part of Fair Value Hedge Remaining to be Amortized			2.8				34.3
Increase (Decrease) in Accrued Investment Income Receivable		300,000		2,300,000
Increase (Decrease) in Interest Payable, Net	2,600,000	10,600,000	7,700,000	45,100,000
Notional Amount Of Derivative Instruments Designated As Investment Hedges	2,000,000,000	1,400,000,000	1,700,000,000	800,000,000
Gain (Loss) on Derivative Used in Net Investment Hedge, Net of Tax	75,100,000	59,200,000	5,900,000	16,600,000
Schedule of Insured Financial Obligations with Credit Deterioration, Insured Contractual Payments Outstanding	158,700,000		158,700,000									246,300,000
Schedule of Insured Financial Obligations with Credit Deterioration, Insured Contractual Payments Outstanding, Principal											154,400,000	226,400,000
Schedule of Insured Financial Obligations with Credit Deterioration, Insured Contractual Payments Outstanding, Interest											4,300,000	19,900,000
Derivative, Remaining Maturity											4.4	5.3
Weighted Average Credit Rating Of Credit Derivatives Outstanding	BB+		BB+		B-
Deficiency Guarantee Government Backing Percent						80.00%
Derivative, Net Liability Position, Aggregate Fair Value											28,500,000	25,900,000
Collateral Paid In Retation To Derivative Agreement													$ 2,100,000