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Derivative Instruments (Credit Derivatives Sold) (Detail) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2016 | Dec. 31, 2015
Credit Default Swap [Member] |  |
Derivative [Line Items] |  |
Weighted average remaining expected maturity | 2 years 1 month 6 days | 2 years 1 month 6 days
Insured Swaps [Member] |  |
Derivative [Line Items] |  |
Weighted average remaining expected maturity | 16 years 6 months 12 days | 16 years 5 months 12 days
Insurance Operations [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | $ 6,409 | $ 6,994
Total fair value of credit derivatives | (102) | (88)
Insurance Operations [Member] | Credit Default Swap [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 2,851 | 3,208
Total fair value of credit derivatives | (99) | (85)
Insurance Operations [Member] | Insured Swaps [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 3,558 | 3,786
Total fair value of credit derivatives | (3) | (3)
Insurance Operations [Member] | Other Credit Derivatives [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount |  | 0
Total fair value of credit derivatives |  | 0
Credit Rating Aaa [Member] | Insurance Operations [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 1,774 | 1,947
Total fair value of credit derivatives |  | 0
Credit Rating Aaa [Member] | Insurance Operations [Member] | Credit Default Swap [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 1,774 | 1,947
Credit Rating Aaa [Member] | Insurance Operations [Member] | Insured Swaps [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount |  | 0
Credit Rating Aaa [Member] | Insurance Operations [Member] | Other Credit Derivatives [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount |  | 0
Credit Rating Aa [Member] | Insurance Operations [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 152 | 109
Total fair value of credit derivatives |  | 0
Credit Rating Aa [Member] | Insurance Operations [Member] | Credit Default Swap [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount |  | 0
Credit Rating Aa [Member] | Insurance Operations [Member] | Insured Swaps [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 152 | 109
Credit Rating Aa [Member] | Insurance Operations [Member] | Other Credit Derivatives [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount |  | 0
Credit Rating A [Member] | Insurance Operations [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 2,351 | 3,015
Total fair value of credit derivatives | (1) | (4)
Credit Rating A [Member] | Insurance Operations [Member] | Credit Default Swap [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 50 | 300
Credit Rating A [Member] | Insurance Operations [Member] | Insured Swaps [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 2,301 | 2,715
Credit Rating A [Member] | Insurance Operations [Member] | Other Credit Derivatives [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount |  | 0
Credit Rating Bbb [Member] | Insurance Operations [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 1,084 | 940
Total fair value of credit derivatives | (2) | (2)
Credit Rating Bbb [Member] | Insurance Operations [Member] | Credit Default Swap [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount |  | 0
Credit Rating Bbb [Member] | Insurance Operations [Member] | Insured Swaps [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 1,084 | 940
Credit Rating Bbb [Member] | Insurance Operations [Member] | Other Credit Derivatives [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount |  | 0
Credit Rating Below Investment Grade [Member] | Insurance Operations [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 1,048 | 983
Total fair value of credit derivatives | (99) | (82)
Credit Rating Below Investment Grade [Member] | Insurance Operations [Member] | Credit Default Swap [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | 1,027 | 961
Credit Rating Below Investment Grade [Member] | Insurance Operations [Member] | Insured Swaps [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount | $ 21 | 22
Credit Rating Below Investment Grade [Member] | Insurance Operations [Member] | Other Credit Derivatives [Member] |  |
Derivative [Line Items] |  |
Derivative notional amount |  | $ 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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=49121117&loc=d3e13433-108611 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4K -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=56946850&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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