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Fair Value Of Financial Instruments (Company's Assets And Liabilities Measured At Fair Value On Recurring Basis) (Detail) - USD ($) $ in Millions | Dec. 31, 2016 | Dec. 31, 2015
--- | --- | ---
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | $ 7,564 |  | $ 9,503
Fair value financial liabilities measured on recurring basis |  | 1,784 |  | 2,918
Variable Interest Entity Primary Beneficiary [Member] | Loan Repurchase Commitments [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 404 |  | 396
Corporate Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 27 |  | 50
Residential Mortgage Backed Non Agency [Member] | Mortgage-backed [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 149 |  | 172
Commercial Mortgage Backed Securities [Member] | Mortgage-backed [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 52 |  | 672
Collateralized Debt Obligations [Member] | Asset-backed [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 8 |  | 14
Other Asset Backed [Member] | Asset-backed [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 19 |  | 24
Money Market Securities [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 521 |  | 354
Loans Receivable At Fair Value [Member] | Variable Interest Entity Primary Beneficiary [Member] | Residential Loans Receivable [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 916 |  | 1,185
Loans Receivable At Fair Value [Member] | Variable Interest Entity Primary Beneficiary [Member] | Other Loans Receivable [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 150 |  | 107
Medium Term Notes [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial liabilities measured on recurring basis |  | 101 |  | 161
Variable Interest Entity Notes [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial liabilities measured on recurring basis |  | 1,351 |  | 2,362
Perpetual Debt And Equity Securities [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 35 |  | 35
Cash And Cash Equivalents [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 163 |  | 464
Cash And Cash Equivalents [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 24 |  | 58
Fixed Income Funds [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis | [1] | 75 |  | 173
Fixed Maturities [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 4,999 |  | 5,785
Fixed Maturities [Member] | U S Treasury And Government [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 937 |  | 976
Fixed Maturities [Member] | State and municipal bonds [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 1,440 |  | 1,726
Fixed Maturities [Member] | Foreign Government Debt [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 9 |  | 198
Fixed Maturities [Member] | Corporate Obligations [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 1,334 |  | 1,457
Fixed Maturities [Member] | Residential Mortgage Backed Agency [Member] | Mortgage-backed [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 868 |  | 993
Fixed Maturities [Member] | Residential Mortgage Backed Non Agency [Member] | Mortgage-backed [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 45 |  | 51
Fixed Maturities [Member] | Commercial Mortgage Backed Securities [Member] | Mortgage-backed [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 43 |  | 31
Fixed Maturities [Member] | Collateralized Debt Obligations [Member] | Asset-backed [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 22 |  | 34
Fixed Maturities [Member] | Other Asset Backed [Member] | Asset-backed [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 301 |  | 319
Derivative Assets [Member] | Interest Rate Derivatives [Member] | Non Insured Derivatives [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 3 |  | 3
Derivative Assets [Member] | Currency Derivatives [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 19 |  | 11
Derivative Liabilities [Member] | Credit Derivatives [Member] | Insured Derivatives [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial liabilities measured on recurring basis |  | 66 |  | 88
Derivative Liabilities [Member] | Interest Rate Derivatives [Member] | Non Insured Derivatives [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial liabilities measured on recurring basis |  | 213 |  | 208
Derivative Liabilities [Member] | Interest Rate Derivatives [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial liabilities measured on recurring basis |  |  |  | 45
Derivative Liabilities [Member] | Other Derivatives [Member] | Non Insured Derivatives [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial liabilities measured on recurring basis |  | 20 |  | 18
Other Liabilities [Member] | Warrant [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial liabilities measured on recurring basis |  | 33 |  | 18
Other Liabilities [Member] | Securities Sold Not Yet Purchased [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial liabilities measured on recurring basis |  |  |  | 18
Fair Value Inputs Level 1 [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 1,559 |  | 1,913
Fair value financial liabilities measured on recurring basis |  | 0 |  | 18
Fair Value Inputs Level 1 [Member] | Money Market Securities [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 521 |  | 354
Fair Value Inputs Level 1 [Member] | Perpetual Debt And Equity Securities [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 26 |  | 18
Fair Value Inputs Level 1 [Member] | Cash And Cash Equivalents [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 163 |  | 464
Fair Value Inputs Level 1 [Member] | Cash And Cash Equivalents [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 24 |  | 58
Fair Value Inputs Level 1 [Member] | Fixed Maturities [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 825 |  | 1,019
Fair Value Inputs Level 1 [Member] | Fixed Maturities [Member] | U S Treasury And Government [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 825 |  | 866
Fair Value Inputs Level 1 [Member] | Fixed Maturities [Member] | Foreign Government Debt [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  |  |  | 153
Fair Value Inputs Level 1 [Member] | Other Liabilities [Member] | Securities Sold Not Yet Purchased [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial liabilities measured on recurring basis |  |  |  | 18
Fair Value Inputs Level 2 [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 4,378 |  | 5,584
Fair value financial liabilities measured on recurring basis |  | 1,123 |  | 1,401
Fair Value Inputs Level 2 [Member] | Corporate Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 27 |  | 39
Fair Value Inputs Level 2 [Member] | Residential Mortgage Backed Non Agency [Member] | Mortgage-backed [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 149 |  | 172
Fair Value Inputs Level 2 [Member] | Commercial Mortgage Backed Securities [Member] | Mortgage-backed [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 52 |  | 672
Fair Value Inputs Level 2 [Member] | Collateralized Debt Obligations [Member] | Asset-backed [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 7 |  | 13
Fair Value Inputs Level 2 [Member] | Other Asset Backed [Member] | Asset-backed [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 18 |  | 18
Fair Value Inputs Level 2 [Member] | Variable Interest Entity Notes [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial liabilities measured on recurring basis |  | 875 |  | 1,095
Fair Value Inputs Level 2 [Member] | Perpetual Debt And Equity Securities [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 9 |  | 17
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 4,113 |  | 4,649
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member] | U S Treasury And Government [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 112 |  | 110
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member] | State and municipal bonds [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 1,440 |  | 1,685
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member] | Foreign Government Debt [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 9 |  | 43
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member] | Corporate Obligations [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 1,332 |  | 1,450
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member] | Residential Mortgage Backed Agency [Member] | Mortgage-backed [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 868 |  | 993
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member] | Residential Mortgage Backed Non Agency [Member] | Mortgage-backed [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 45 |  | 51
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member] | Commercial Mortgage Backed Securities [Member] | Mortgage-backed [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 43 |  | 31
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member] | Collateralized Debt Obligations [Member] | Asset-backed [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 7 |  | 5
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member] | Other Asset Backed [Member] | Asset-backed [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 257 |  | 281
Fair Value Inputs Level 2 [Member] | Derivative Assets [Member] | Interest Rate Derivatives [Member] | Non Insured Derivatives [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 3 |  | 4
Fair Value Inputs Level 2 [Member] | Derivative Liabilities [Member] | Credit Derivatives [Member] | Insured Derivatives [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial liabilities measured on recurring basis |  | 2 |  | 3
Fair Value Inputs Level 2 [Member] | Derivative Liabilities [Member] | Interest Rate Derivatives [Member] | Non Insured Derivatives [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial liabilities measured on recurring basis |  | 213 |  | 240
Fair Value Inputs Level 2 [Member] | Derivative Liabilities [Member] | Interest Rate Derivatives [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial liabilities measured on recurring basis |  |  |  | 45
Fair Value Inputs Level 2 [Member] | Other Liabilities [Member] | Warrant [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial liabilities measured on recurring basis |  | 33 |  | 18
Fair Value Inputs Level 3 [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 1,552 |  | 1,834
Fair value financial liabilities measured on recurring basis |  | 661 |  | 1,531
Fair Value Inputs Level 3 [Member] | Variable Interest Entity Primary Beneficiary [Member] | Loan Repurchase Commitments [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 404 |  | 396
Fair Value Inputs Level 3 [Member] | Corporate Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis | [2] |  |  | 11
Fair Value Inputs Level 3 [Member] | Collateralized Debt Obligations [Member] | Asset-backed [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis | [2] | 1 |  | 1
Fair Value Inputs Level 3 [Member] | Other Asset Backed [Member] | Asset-backed [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis | [2] | 1 |  | 6
Fair Value Inputs Level 3 [Member] | Loans Receivable At Fair Value [Member] | Variable Interest Entity Primary Beneficiary [Member] | Residential Loans Receivable [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 916 |  | 1,185
Fair Value Inputs Level 3 [Member] | Loans Receivable At Fair Value [Member] | Variable Interest Entity Primary Beneficiary [Member] | Other Loans Receivable [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 150 | [2] | 107
Fair Value Inputs Level 3 [Member] | Medium Term Notes [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial liabilities measured on recurring basis | [2] | 101 |  | 161
Fair Value Inputs Level 3 [Member] | Variable Interest Entity Notes [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial liabilities measured on recurring basis |  | 476 |  | 1,267
Fair Value Inputs Level 3 [Member] | Fixed Maturities [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 61 |  | 117
Fair Value Inputs Level 3 [Member] | Fixed Maturities [Member] | State and municipal bonds [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis | [2] |  |  | 41
Fair Value Inputs Level 3 [Member] | Fixed Maturities [Member] | Foreign Government Debt [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis | [2] |  |  | 2
Fair Value Inputs Level 3 [Member] | Fixed Maturities [Member] | Corporate Obligations [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis | [2] | 2 |  | 7
Fair Value Inputs Level 3 [Member] | Fixed Maturities [Member] | Collateralized Debt Obligations [Member] | Asset-backed [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis | [2] | 15 |  | 29
Fair Value Inputs Level 3 [Member] | Fixed Maturities [Member] | Other Asset Backed [Member] | Asset-backed [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis | [2] | 44 |  | 38
Fair Value Inputs Level 3 [Member] | Derivative Assets [Member] | Currency Derivatives [Member] | Variable Interest Entity Primary Beneficiary [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis | [2] | 19 |  | 11
Fair Value Inputs Level 3 [Member] | Derivative Liabilities [Member] | Credit Derivatives [Member] | Insured Derivatives [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial liabilities measured on recurring basis |  | 64 |  | 85
Fair Value Inputs Level 3 [Member] | Derivative Liabilities [Member] | Other Derivatives [Member] | Non Insured Derivatives [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial liabilities measured on recurring basis |  | 20 |  | 18
Counterparty And Cash Collateral Netting [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  | 0 |  | (1)
Fair value financial liabilities measured on recurring basis |  | $ 0 |  | (32)
Counterparty And Cash Collateral Netting [Member] | Derivative Assets [Member] | Interest Rate Derivatives [Member] | Non Insured Derivatives [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial assets measured on recurring basis |  |  |  | (1)
Counterparty And Cash Collateral Netting [Member] | Derivative Liabilities [Member] | Interest Rate Derivatives [Member] | Non Insured Derivatives [Member] |  |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |  |
Fair value financial liabilities measured on recurring basis |  |  |  | $ (32)
[1] | Investment was measured at fair value by applying the net asset value per share practical expedient, and was not classified in the fair value hierarchy in accordance with ASC 820-10. The fair value amount presented was provided to permit reconciliation of the fair value of assets categorized within the fair value hierarchy to the amounts presented in the statement of financial position.
[2] | Unobservable inputs are either not developed by the Company or do not significantly impact the overall fair values of the aggregate financial assets and liabilities.

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