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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 | Mar. 31, 2016 | Dec. 31, 2015
--- | --- | ---
Accounts Notes And Loans Receivable [Line Items] |  |  |
Fair value financial assets measured on recurring basis |  | $ 9,457 | $ 9,503
Fair value financial liabilities measured on recurring basis |  | 2,795 | 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 |  | 399 | 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 |  | 39 | 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 |  | 161 | 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 |  | 615 | 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 |  | 13 | 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 |  | 20 | 24
Money Market Securities [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Fair value financial assets measured on recurring basis |  | 207 | 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 |  | 1,115 | 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 |  | 253 | 107
Medium Term Notes [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Fair value financial liabilities measured on recurring basis |  | 165 | 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 |  | 2,204 | 2,362
Perpetual Debt And Equity Securities [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Fair value financial assets measured on recurring basis |  | 210 | 208
Cash And Cash Equivalents [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Fair value financial assets measured on recurring basis |  | 285 | 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 |  | 47 | 58
Fixed Maturities [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Fair value financial assets measured on recurring basis |  | 6,085 | 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 |  | 1,226 | 976
Fixed Maturities [Member] | State and municipal bonds [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Fair value financial assets measured on recurring basis |  | 1,646 | 1,726
Fixed Maturities [Member] | Foreign Government Debt [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Fair value financial assets measured on recurring basis |  | 189 | 198
Fixed Maturities [Member] | Corporate Obligations [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Fair value financial assets measured on recurring basis |  | 1,589 | 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 |  | 968 | 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 |  | 49 | 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 |  | 29 | 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 |  | 30 | 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 |  | 359 | 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 |  | 5 | 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 |  | 102 | 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 |  | 237 | 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 |  | 36 | 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 |  | 19 | 18
Other Liabilities [Member] | Warrant [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Fair value financial liabilities measured on recurring basis |  | 29 | 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 |  | 3 | 18
Fair Value Inputs Level 1 [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Fair value financial assets measured on recurring basis |  | 1,823 | 1,913
Fair value financial liabilities measured on recurring basis |  | 3 | 18
Fair Value Inputs Level 1 [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 |  | 2 |
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 |  | 207 | 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 |  | 22 | 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 |  | 285 | 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 |  | 47 | 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 |  | 1,260 | 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 |  | 1,111 | 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 |  | 149 | 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 |  | 3 | 18
Fair Value Inputs Level 2 [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Fair value financial assets measured on recurring basis |  | 5,785 | 5,757
Fair value financial liabilities measured on recurring basis |  | 1,378 | 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 |  | 38 | 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 |  | 161 | 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 |  | 611 | 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 |  | 12 | 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 |  | 17 | 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 |  | 1,028 | 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 |  | 188 | 190
Fair Value Inputs Level 2 [Member] | Fixed Maturities [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Fair value financial assets measured on recurring basis |  | 4,754 | 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 |  | 115 | 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 |  | 1,643 | 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 |  | 38 | 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 |  | 1,588 | 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 |  | 968 | 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 |  | 49 | 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 |  | 29 | 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 |  | 4 | 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 |  | 320 | 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 |  | 4 | 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 |  | 3 | 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 |  | 282 | 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 |  | 36 | 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 |  | 29 | 18
Fair Value Inputs Level 3 [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Fair value financial assets measured on recurring basis |  | 1,850 | 1,834
Fair value financial liabilities measured on recurring basis |  | 1,459 | 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 |  | 399 | 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 | [1] | 1 | 11
Fair Value Inputs Level 3 [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 | [1] | 0 |
Fair Value Inputs Level 3 [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 |  | 2 |
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 | [1] | 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 | [1] | 3 | 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 |  | 1,115 | 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 |  | 253 | 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 | [1] | 165 | 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 |  | 1,176 | 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 |  | 71 | 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 | [1] | 3 | 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 | [1] | 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 | [1] | 1 | 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 | [1] | 26 | 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 | [1] | 39 | 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 |  | 5 | 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 |  | 99 | 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 |  | 19 | 18
Counterparty And Cash Collateral Netting [Member] |  |  |
Accounts Notes And Loans Receivable [Line Items] |  |  |
Fair value financial assets measured on recurring basis |  | (1) | (1)
Fair value financial liabilities measured on recurring basis |  | (45) | (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) | (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 |  | $ (45) | $ (32)
[1] | 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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