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Investments (Securities Held In Unrealized Loss Position And Insured By Financial Guarantor) (Detail) $ in Millions | Dec. 31, 2018 USD ($)
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Schedule Of Investments [Line Items] |  |
Total Available-For-Sale, Fair Value | $ 2,420 |
Financial Guarantee [Member] |  |
Schedule Of Investments [Line Items] |  |
Total Available-For-Sale, Fair Value | 95 |
Gross unrealized losses | (12) |
Loss and loss adjustment expense reserves | 15 | [1]
Mortgage-backed [Member] | Mbia Corp And National [Member] | Financial Guarantee [Member] |  |
Schedule Of Investments [Line Items] |  |
Total Available-For-Sale, Fair Value | 13 | [2]
Gross unrealized losses | (4) | [2]
Loss and loss adjustment expense reserves | 15 | [1],[2]
Corporate Obligations [Member] | Mbia Corp And National [Member] | Financial Guarantee [Member] |  |
Schedule Of Investments [Line Items] |  |
Total Available-For-Sale, Fair Value | 81 | [2]
Gross unrealized losses | (8) | [2]
Loss and loss adjustment expense reserves | 0 | [1],[2]
All Other Securities [Member] | Financial Guarantee [Member] |  |
Schedule Of Investments [Line Items] |  |
Total Available-For-Sale, Fair Value | 1 |
Gross unrealized losses | 0 |
Loss and loss adjustment expense reserves | 0 |
All Other Securities [Member] | Mbia Corp And National [Member] | Financial Guarantee [Member] |  |
Schedule Of Investments [Line Items] |  |
Total Available-For-Sale, Fair Value | 0 | [2]
Gross unrealized losses | 0 | [2]
Loss and loss adjustment expense reserves | 0 | [1],[2]
All Other Securities [Member] | Other Insurers [Member] | Financial Guarantee [Member] |  |
Schedule Of Investments [Line Items] |  |
Total Available-For-Sale, Fair Value | 1 |
Gross unrealized losses | 0 |
Loss and loss adjustment expense reserves | $ 0 | [1]
[1] | Insurance loss reserve estimates are based on the proportion of par value owned to the total amount of par value insured.
[2] | Includes investments insured by MBIA Corp. and National.

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- Definition Amount of accumulated pre-tax unrealized losses before deducting pre-tax unrealized gains on investments in available-for-sale securities impacting investments. + References No definition available. + Details
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- Definition The amount needed to reflect the estimated ultimate cost of settling claims relating to insured events by financial guarantor that have occurred on or before the balance sheet date, whether or not reported to the insurer at that date. + References No definition available. + Details
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- Definition This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities. + References No definition available. + Details
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