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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 | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) Y
--- | --- | ---
Other Derivative Liabilities [Member] | Discounted cash flow [Member] |  |  |
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] |  |  |
Fair value, liabilities |  | $ 4 | $ 20
Nonperformance Risk [Member] | Commercial Mortgage Backed Securities [Member] | Minimum [Member] | Direct Price Model [Member] |  |  |
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] |  |  |
Range percentage |  | 54.00% |
Nonperformance Risk [Member] | Commercial Mortgage Backed Securities [Member] | Maximum [Member] | Direct Price Model [Member] |  |  |
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] |  |  |
Range percentage |  | 54.00% |
Nonperformance Risk [Member] | Commercial Mortgage Backed Securities [Member] | Weighted Average [Member] | Direct Price Model [Member] |  |  |
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] |  |  |
Range percentage |  | 54.00% |
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 |  | 49 | 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 | [1] | 25 | 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 |  |  | 62
Credit Derivatives [Member] | Commercial Mortgage Backed Securities [Member] | Direct Price Model [Member] |  |  |
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] |  |  |
Fair value, liabilities |  | 63 |
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 |  |  | $ 2
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%
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 |  |  | 40.00%
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 |  |  | 33.00%
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 |  |  | 10.00%
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 |  |  | 32.00%
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 |  |  | 32.00%
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 |  |  | 58.00%
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 |  |  | 58.00%
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 |  |  | 58.00%
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
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 |  |  | 1.5
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 |  |  | 1.3
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 |  |  | 25.00%
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 |  |  | 35.00%
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 |  |  | 30.00%
Loans Receivable [Member] | Variable Interest Entity Primary Beneficiary [Member] | Quoted market prices adjusted for financial guarantees provided to VIE obligations and multiples of EBITDA [Member] |  |  |
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] |  |  |
Fair Value, assets |  | $ 1,679 | $ 916
Loans Receivable [Member] | Variable Interest Entity Primary Beneficiary [Member] | Impact Of Financial Guarantee [Member] | Minimum [Member] | Quoted market prices adjusted for financial guarantees provided to VIE obligations and multiples of EBITDA [Member] |  |  |
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] |  |  |
Range percentage |  | (25.00%) | 0.00%
Loans Receivable [Member] | Variable Interest Entity Primary Beneficiary [Member] | Impact Of Financial Guarantee [Member] | Maximum [Member] | Quoted market prices adjusted for financial guarantees provided to VIE obligations and multiples of EBITDA [Member] |  |  |
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] |  |  |
Range percentage |  | 35.00% | 28.00%
Loans Receivable [Member] | Variable Interest Entity Primary Beneficiary [Member] | Impact Of Financial Guarantee [Member] | Weighted Average [Member] | Quoted market prices adjusted for financial guarantees provided to VIE obligations and multiples of EBITDA [Member] |  |  |
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] |  |  |
Range percentage |  | (2.00%) | 3.00%
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 |  | $ 407 | $ 404
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 |  | $ 406 | $ 476
Variable Interest Entity Notes [Member] | Variable Interest Entity Primary Beneficiary [Member] | Impact Of Financial Guarantee [Member] | Minimum [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] |  |  |
Range percentage |  | 0.00% | 0.00%
Variable Interest Entity Notes [Member] | Variable Interest Entity Primary Beneficiary [Member] | Impact Of Financial Guarantee [Member] | Maximum [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] |  |  |
Range percentage |  | 60.00% | 54.00%
Variable Interest Entity Notes [Member] | Variable Interest Entity Primary Beneficiary [Member] | Impact Of Financial Guarantee [Member] | Weighted Average [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] |  |  |
Range percentage |  | 36.00% | 24.00%
[1] | Midpoint of cash flows are used for the weighted average.

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- Definition Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
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