Fair Value Of Financial Instruments (Quantitative Information Regarding The Significant Unobservable Inputs For Certain Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Detail) $ in Millions	Jun. 30, 2015 USD ($) Y	Dec. 31, 2014 USD ($) Y
Other Derivative Liabilities [Member] | Discounted cash flow [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value, liabilities	$ 21	$ 24
Discounted Cash Flows [Member] | Other Derivative Liabilities [Member] | Minimum [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range dollars	0	0
Discounted Cash Flows [Member] | Other Derivative Liabilities [Member] | Maximum [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range dollars	83	83
Discounted Cash Flows [Member] | Other Derivative Liabilities [Member] | Weighted Average [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range dollars	42	42
Credit Derivatives [Member] | Commercial Mortgage Backed Securities [Member] | BET Model [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value, liabilities	128	224
Credit Derivatives [Member] | Multi Sector C D O [Member] | Direct Price Model [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value, liabilities	4	9
Credit Derivatives [Member] | Other Derivative Liabilities [Member] | BET And Dual Default Valuation Models [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value, liabilities	$ 12	$ 11
Credit Derivatives [Member] | Recovery Rates [Member] | Commercial Mortgage Backed Securities [Member] | Minimum [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range percentage	25.00%	25.00%
Credit Derivatives [Member] | Recovery Rates [Member] | Commercial Mortgage Backed Securities [Member] | Maximum [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range percentage	90.00%	90.00%
Credit Derivatives [Member] | Recovery Rates [Member] | Commercial Mortgage Backed Securities [Member] | Weighted Average [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range percentage	65.00%	59.00%
Credit Derivatives [Member] | Recovery Rates [Member] | Other Derivative Liabilities [Member] | Minimum [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range percentage	42.00%	42.00%
Credit Derivatives [Member] | Recovery Rates [Member] | Other Derivative Liabilities [Member] | Maximum [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range percentage	45.00%	45.00%
Credit Derivatives [Member] | Recovery Rates [Member] | Other Derivative Liabilities [Member] | Weighted Average [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range percentage	45.00%	45.00%
Credit Derivatives [Member] | Nonperformance Risk [Member] | Commercial Mortgage Backed Securities [Member] | Minimum [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range percentage	15.00%	12.00%
Credit Derivatives [Member] | Nonperformance Risk [Member] | Commercial Mortgage Backed Securities [Member] | Maximum [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range percentage	29.00%	29.00%
Credit Derivatives [Member] | Nonperformance Risk [Member] | Commercial Mortgage Backed Securities [Member] | Weighted Average [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range percentage	23.00%	25.00%
Credit Derivatives [Member] | Nonperformance Risk [Member] | Multi Sector C D O [Member] | Minimum [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range percentage	47.00%	53.00%
Credit Derivatives [Member] | Nonperformance Risk [Member] | Multi Sector C D O [Member] | Maximum [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range percentage	47.00%	53.00%
Credit Derivatives [Member] | Nonperformance Risk [Member] | Multi Sector C D O [Member] | Weighted Average [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range percentage	47.00%	53.00%
Credit Derivatives [Member] | Nonperformance Risk [Member] | Other Derivative Liabilities [Member] | Minimum [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range percentage	47.00%	41.00%
Credit Derivatives [Member] | Nonperformance Risk [Member] | Other Derivative Liabilities [Member] | Maximum [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range percentage	47.00%	51.00%
Credit Derivatives [Member] | Nonperformance Risk [Member] | Other Derivative Liabilities [Member] | Weighted Average [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range percentage	47.00%	50.00%
Credit Derivatives [Member] | Weighted Average Life [Member] | Commercial Mortgage Backed Securities [Member] | Minimum [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Weighted Average (in years) | Y	1	1.3
Credit Derivatives [Member] | Weighted Average Life [Member] | Commercial Mortgage Backed Securities [Member] | Maximum [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Weighted Average (in years) | Y	2	3.2
Credit Derivatives [Member] | Weighted Average Life [Member] | Commercial Mortgage Backed Securities [Member] | Weighted Average [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Weighted Average (in years) | Y	1.5	2.3
Credit Derivatives [Member] | Weighted Average Life [Member] | Other Derivative Liabilities [Member] | Minimum [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Weighted Average (in years) | Y	0.3	0.2
Credit Derivatives [Member] | Weighted Average Life [Member] | Other Derivative Liabilities [Member] | Maximum [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Weighted Average (in years) | Y	7.6	7.9
Credit Derivatives [Member] | Weighted Average Life [Member] | Other Derivative Liabilities [Member] | Weighted Average [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Weighted Average (in years) | Y	0.8	1.1
Credit Derivatives [Member] | Commercial Mortgage Backed Securities Spreads [Member] | Commercial Mortgage Backed Securities [Member] | Minimum [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range percentage	0.00%	0.00%
Credit Derivatives [Member] | Commercial Mortgage Backed Securities Spreads [Member] | Commercial Mortgage Backed Securities [Member] | Maximum [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range percentage	62.00%	41.00%
Credit Derivatives [Member] | Commercial Mortgage Backed Securities Spreads [Member] | Commercial Mortgage Backed Securities [Member] | Weighted Average [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range percentage	20.00%	19.00%
Loans Receivable [Member] | Variable Interest Entity Primary Beneficiary [Member] | Quoted market prices adjusted for financial guarantees provided to VIE obligations [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair Value, assets	$ 1,426	$ 1,431
Loans Receivable [Member] | Variable Interest Entity Primary Beneficiary [Member] | Impact Of Financial Guarantee [Member] | Minimum [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range percentage	0.00%	0.00%
Loans Receivable [Member] | Variable Interest Entity Primary Beneficiary [Member] | Impact Of Financial Guarantee [Member] | Maximum [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range percentage	6.00%	10.00%
Loans Receivable [Member] | Variable Interest Entity Primary Beneficiary [Member] | Impact Of Financial Guarantee [Member] | Weighted Average [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range percentage	2.00%	2.00%
Loan Repurchase Commitments [Member] | Variable Interest Entity Primary Beneficiary [Member] | Discounted cash flow [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair Value, assets	$ 388	$ 379
Variable Interest Entity Notes [Member] | Variable Interest Entity Primary Beneficiary [Member] | Quoted market prices of VIE assets adjusted for financial guarantees provided [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value, liabilities	$ 1,374	$ 735
Variable Interest Entity Notes [Member] | Variable Interest Entity Primary Beneficiary [Member] | Impact Of Financial Guarantee [Member] | Minimum [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range percentage	0.00%	0.00%
Variable Interest Entity Notes [Member] | Variable Interest Entity Primary Beneficiary [Member] | Impact Of Financial Guarantee [Member] | Maximum [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range percentage	41.00%	35.00%
Variable Interest Entity Notes [Member] | Variable Interest Entity Primary Beneficiary [Member] | Impact Of Financial Guarantee [Member] | Weighted Average [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Range percentage	9.00%	16.00%