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Derivative Instruments (Credit Derivatives Sold) (Detail) - Insurance Operations [Member] - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018
Derivative [Line Items] |  |
Derivative notional amount | $ 1,827 | $ 2,503
Total fair value of credit derivatives | $ (9) | $ (35)
Credit Default Swap [Member] |  |
Derivative [Line Items] |  |
Weighted average remaining expected maturity | 1 year | 1 year
Derivative notional amount | $ 32 | $ 70
Total fair value of credit derivatives | $ (7) | $ (33)
Insured Swaps [Member] |  |
Derivative [Line Items] |  |
Weighted average remaining expected maturity | 14 years 7 months 6 days | 15 years 8 months 12 days
Derivative notional amount | $ 1,795 | $ 2,433
Total fair value of credit derivatives | (2) | (2)
Credit Rating Aaa [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 0 | 0
Total fair value of credit derivatives | 0 | 0
Credit Rating Aaa [Member] | Credit Default Swap [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 0 | 0
Credit Rating Aaa [Member] | Insured Swaps [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 0 | 0
Credit Rating Aa [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 66 | 74
Total fair value of credit derivatives | 0 | 0
Credit Rating Aa [Member] | Credit Default Swap [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 0 | 0
Credit Rating Aa [Member] | Insured Swaps [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 66 | 74
Credit Rating A [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 1,284 | 1,463
Total fair value of credit derivatives | (1) | (1)
Credit Rating A [Member] | Credit Default Swap [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 0 | 0
Credit Rating A [Member] | Insured Swaps [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 1,284 | 1,463
Credit Rating Bbb [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 445 | 896
Total fair value of credit derivatives | (1) | (1)
Credit Rating Bbb [Member] | Credit Default Swap [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 0 | 0
Credit Rating Bbb [Member] | Insured Swaps [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 445 | 896
Credit Rating Below Investment Grade [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 32 | 70
Total fair value of credit derivatives | (7) | (33)
Credit Rating Below Investment Grade [Member] | Credit Default Swap [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 32 | 70
Credit Rating Below Investment Grade [Member] | Insured Swaps [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | $ 0 | $ 0

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