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Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Millions | Dec. 31, 2019 | Sep. 30, 2019 | Dec. 31, 2018
--- | --- | --- | ---
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Other Investments | $ 478 |  | $ 391
Credit valuation adjustment included in fair value of credit derivative liabilities | 0 |  | 0
Fair value of derivative liabilities | 89 |  |
Derivative liabilities | $ 90 |  | $ 77
Weighted average discounted rate of estimated future premium payments to be paid by the VIEs | 2.40% |  | 2.70%
Fixed Income Securities [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Percentage of investment portfolio valued using dealer quotes | 4.00% |  | 8.00%
Asset-backed Securities [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Coupon rate | 5.97% |  | 5.97%
European ABS Transactions [Member] | Level 3 [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Fair value of consolidated VIE debt obligations valued using unobservable inputs by asset class | $ 0 |  | $ 217
Minimum [Member] | Fixed Income Securities [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Percentage of investment portfolio valued using internal valuation models | 2.00% |  | 2.00%
Maximum [Member] | Fixed Income Securities [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Percentage of investment portfolio valued using external pricing services | 94.00% |  | 90.00%
Variable Interest Entity, Primary Beneficiary [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Fair value of derivative liabilities | $ 0 |  |
Derivative liabilities | $ 1,657 |  | $ 1,712
Weighted average discounted rate of estimated future premium payments to be paid by the VIEs | 2.70% |  | 3.10%
Variable Interest Entity, Primary Beneficiary [Member] | European ABS Transactions [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Coupon rate |  |  | 2.20%
Real Estate [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Other Investments | $ 16 |  | $ 16
Hedge Funds, Multi-strategy [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Other Investments |  | $ 65 | 0
Interest Rate Contract [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Other Investments | 176 |  | 114
Illiquid Investments [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Other Investments | $ 51 |  | 84
Other Credit Derivatives [Member] | Level 3 [Member] |  |  |
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items] |  |  |
Derivative liabilities |  |  | $ 1

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