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	12 Months Ended
	Dec. 31, 2012
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	$ 1,590
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	525
Credit Derivatives [Member] | Other [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Valuation Techniques	BET Model
Fair Value	806
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	1,881
Loans Receivable [Member] | Variable Interest Entity [Member] | Impact Of Financial Guarantee Asset [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 Asset [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	14.00%
Loans Receivable [Member] | Variable Interest Entity [Member] | Impact Of Financial Guarantee Asset [Member] | Weighted Average [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	3.00%
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	1,086
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	10.00%
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	75.00%
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	47.00%
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	66.00%
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	$ 1,932
Variable Interest Entity Notes [Member] | Variable Interest Entity [Member] | Impact Of Financial Guarantee Liability [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 Liability [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	23.00%
Variable Interest Entity Notes [Member] | Variable Interest Entity [Member] | Impact Of Financial Guarantee Liability [Member] | Weighted Average [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	6.00%
Credit Derivative Liabilities [Member] | Commercial Mortgage-Backed [Member] | Recovery Rates [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	21.00%
Credit Derivative Liabilities [Member] | 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%
Credit Derivative Liabilities [Member] | 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%
Credit Derivative Liabilities [Member] | Commercial Mortgage-Backed [Member] | Nonperformance Risk [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	19.00%
Credit Derivative Liabilities [Member] | Commercial Mortgage-Backed [Member] | Nonperformance Risk [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	59.00%
Credit Derivative Liabilities [Member] | Commercial Mortgage-Backed [Member] | Nonperformance Risk [Member] | Weighted Average [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	58.00%
Credit Derivative Liabilities [Member] | 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)	0.1
Credit Derivative Liabilities [Member] | 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)	5.6
Credit Derivative Liabilities [Member] | 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)	4.4
Credit Derivative Liabilities [Member] | 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%
Credit Derivative Liabilities [Member] | Commercial Mortgage-Backed [Member] | CMBS Spreads [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	23.00%
Credit Derivative Liabilities [Member] | Commercial Mortgage-Backed [Member] | CMBS Spreads [Member] | Weighted Average [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	13.00%
Credit Derivative Liabilities [Member] | Multi-Sector CDO [Member] | Nonperformance Risk [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	59.00%
Credit Derivative Liabilities [Member] | Multi-Sector CDO [Member] | Nonperformance Risk [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	59.00%
Credit Derivative Liabilities [Member] | Multi-Sector CDO [Member] | Nonperformance Risk [Member] | Weighted Average [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	59.00%
Credit Derivative Liabilities [Member] | Other [Member] | Recovery Rates [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	42.00%
Credit Derivative Liabilities [Member] | Other [Member] | Recovery Rates [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	75.00%
Credit Derivative Liabilities [Member] | Other [Member] | Recovery Rates [Member] | Weighted Average [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	47.00%
Credit Derivative Liabilities [Member] | Other [Member] | Nonperformance Risk [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	42.00%
Credit Derivative Liabilities [Member] | Other [Member] | Nonperformance Risk [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	59.00%
Credit Derivative Liabilities [Member] | Other [Member] | Nonperformance Risk [Member] | Weighted Average [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range Percentage	58.00%
Credit Derivative Liabilities [Member] | Other [Member] | Weighted Average Life [Member] | Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range (in years)	0.1
Credit Derivative Liabilities [Member] | Other [Member] | Weighted Average Life [Member] | Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range (in years)	19.6
Credit Derivative Liabilities [Member] | Other [Member] | Weighted Average Life [Member] | Weighted Average [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Range (in years)	3.0