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Derivative Instruments (Credit Derivatives Sold) (Detail) - Insurance Operations [Member] - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2019 | Dec. 31, 2018
Derivative [Line Items] |  |
Derivative notional amount | $ 2,116 | $ 2,503
Total fair value of credit derivatives | $ (21) | $ (35)
Credit Default Swap [Member] |  |
Derivative [Line Items] |  |
Weighted average remaining expected maturity | 9 months 18 days | 1 year
Derivative notional amount | $ 53 | $ 70
Total fair value of credit derivatives | $ (19) | $ (33)
Insured Swaps [Member] |  |
Derivative [Line Items] |  |
Weighted average remaining expected maturity | 15 years 6 months | 15 years 8 months 12 days
Derivative notional amount | $ 2,063 | $ 2,433
Total fair value of credit derivatives | (2) | (2)
Insured Swaps - Held for Sale [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 0 | 0
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 Aaa [Member] | Other Credit Derivatives [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 0 |
Credit Rating Aa [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 72 | 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 | 72 | 74
Credit Rating Aa [Member] | Other Credit Derivatives [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 0 |
Credit Rating A [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 1,436 | 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 | 1,436 | 1,463
Credit Rating A [Member] | Other Credit Derivatives [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 0 |
Credit Rating Bbb [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 555 | 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 | 555 | 896
Credit Rating Bbb [Member] | Insured Swaps - Held for Sale [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 0 | 0
Credit Rating Below Investment Grade [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 53 | 70
Total fair value of credit derivatives | (19) | (33)
Credit Rating Below Investment Grade [Member] | Credit Default Swap [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 53 | 70
Credit Rating Below Investment Grade [Member] | Insured Swaps [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | $ 0 | $ 0

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- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
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- Definition Weighted Average Remaining Maturity Credit Derivatives In Years + References No definition available. + Details
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- Definition Fair value of credit risk derivative liability. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4K -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5708775-113959 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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