Fair Value Of Financial Instruments (Quantitative Information Regarding Significant Unobservable Inputs For Assets And Liabilities Measured At Fair Value On Recurring Basis) (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012
Commercial Mortgage-Backed [Member] | Recovery Rates [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	20.00%
Commercial Mortgage-Backed [Member] | Recovery Rates [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	90.00%
Commercial Mortgage-Backed [Member] | Recovery Rates [Member] | Weighted Average [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	51.00%
Commercial Mortgage-Backed [Member] | Nonperformance Risk [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	8.00%
Commercial Mortgage-Backed [Member] | Nonperformance Risk [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	62.00%
Commercial Mortgage-Backed [Member] | Nonperformance Risk [Member] | Weighted Average [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	57.00%
Commercial Mortgage-Backed [Member] | Weighted Average Life [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range (in years)	0.3
Commercial Mortgage-Backed [Member] | Weighted Average Life [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range (in years)	5.9
Commercial Mortgage-Backed [Member] | Weighted Average Life [Member] | Weighted Average [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range (in years)	4.6
Commercial Mortgage-Backed [Member] | CMBS Spreads [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	1.00%
Commercial Mortgage-Backed [Member] | CMBS Spreads [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	22.00%
Commercial Mortgage-Backed [Member] | CMBS Spreads [Member] | Weighted Average [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	12.00%
Multi-Sector CDO [Member] | Nonperformance Risk [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	63.00%
Multi-Sector CDO [Member] | Nonperformance Risk [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	63.00%
Multi-Sector CDO [Member] | Nonperformance Risk [Member] | Weighted Average [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	63.00%
Other [Member] | Recovery Rates [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	42.00%
Other [Member] | Recovery Rates [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	75.00%
Other [Member] | Recovery Rates [Member] | Weighted Average [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	47.00%
Other [Member] | Nonperformance Risk [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	8.00%
Other [Member] | Nonperformance Risk [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	63.00%
Other [Member] | Nonperformance Risk [Member] | Weighted Average [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	50.00%
Other [Member] | Weighted Average Life [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range (in years)	0.2
Other [Member] | Weighted Average Life [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range (in years)	19
Other [Member] | Weighted Average Life [Member] | Weighted Average [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range (in years)	3.1
Credit Derivatives [Member] | Commercial Mortgage-Backed [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Valuation Techniques	BET Model
Fair Value	$ 1,533
Credit Derivatives [Member] | Multi-Sector CDO [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Valuation Techniques	Direct Price Model
Fair Value	628
Credit Derivatives [Member] | Other [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Valuation Techniques	BET Model
Fair Value	1,156
Loans Receivable [Member] | Variable Interest Entity [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Valuation Techniques	Quoted market prices adjusted for financial guarantees provided to VIE obligations
Fair Value	1,892
Loans Receivable [Member] | Variable Interest Entity [Member] | Impact Of Financial Guarantee [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	0.00%
Loans Receivable [Member] | Variable Interest Entity [Member] | Impact Of Financial Guarantee [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	22.00%
Loans Receivable [Member] | Variable Interest Entity [Member] | Impact Of Financial Guarantee [Member] | Weighted Average [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	4.00%
Loan Repurchase Commitments [Member] | Variable Interest Entity [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Valuation Techniques	Discounted cash flow
Fair Value	1,051
Loan Repurchase Commitments [Member] | Variable Interest Entity [Member] | Recovery Rates [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	9.00%
Loan Repurchase Commitments [Member] | Variable Interest Entity [Member] | Recovery Rates [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	96.00%
Loan Repurchase Commitments [Member] | Variable Interest Entity [Member] | Recovery Rates [Member] | Weighted Average [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	43.00%
Loan Repurchase Commitments [Member] | Variable Interest Entity [Member] | Breach Rates [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	65.00%
Loan Repurchase Commitments [Member] | Variable Interest Entity [Member] | Breach Rates [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	94.00%
Loan Repurchase Commitments [Member] | Variable Interest Entity [Member] | Breach Rates [Member] | Weighted Average [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	78.00%
Variable Interest Entity Notes [Member] | Variable Interest Entity [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Valuation Techniques	Quoted market prices of VIE assets adjusted for financial guarantees provided
Fair Value, liabilities	$ 1,885
Variable Interest Entity Notes [Member] | Variable Interest Entity [Member] | Impact Of Financial Guarantee [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	0.00%
Variable Interest Entity Notes [Member] | Variable Interest Entity [Member] | Impact Of Financial Guarantee [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	20.00%
Variable Interest Entity Notes [Member] | Variable Interest Entity [Member] | Impact Of Financial Guarantee [Member] | Weighted Average [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	6.00%