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Fair Value Measurements (Fair Value And Maximum Future Funding Commitments Related To Investments) (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Fair Value | $ 3,623 | $ 3,627
Maximum future funding commitment | 4,061 | 2,040
Financial |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Fair Value | 540 | 548
Maximum future funding commitment | $ 330 | $ 428
Financial | Minimum |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Expected liquidation period | 5 years | 5 years
Financial | Maximum |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Expected liquidation period | 9 years | 9 years
Real Assets |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Fair Value | $ 651 | $ 536
Maximum future funding commitment | $ 114 | $ 230
Real Assets | Minimum |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Expected liquidation period | 3 years | 3 years
Real Assets | Maximum |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Expected liquidation period | 7 years | 7 years
Distressed |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Fair Value | $ 289 | $ 485
Maximum future funding commitment | $ 141 | $ 179
Distressed | Minimum |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Expected liquidation period | 3 years | 3 years
Distressed | Maximum |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Expected liquidation period | 7 years | 7 years
Private Credit |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Fair Value | $ 187 | $ 236
Maximum future funding commitment | $ 327 | $ 259
Private Credit | Minimum |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Expected liquidation period | 3 years | 3 years
Private Credit | Maximum |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Expected liquidation period | 7 years | 7 years
Traditional |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Fair Value | $ 1,656 | $ 1,550
Maximum future funding commitment | $ 3,149 | $ 930
Traditional | Minimum |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Expected liquidation period | 3 years | 3 years
Traditional | Maximum |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Expected liquidation period | 15 years | 15 years
Vintage |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Fair Value | $ 30 | $ 21
Maximum future funding commitment |  | $ 14
Vintage | Minimum |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Expected liquidation period | 1 year | 1 year
Vintage | Maximum |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Expected liquidation period | 2 years | 2 years
Investment Funds |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Fair Value | $ 270 | $ 251

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- Definition Fair value of investment in certain entities that calculate net asset value per share. Includes, but is not limited to, by unit, membership interest, or other ownership interest. Investment includes, but is not limited to, investment in certain hedge funds, venture capital funds, private equity funds, real estate partnerships or funds. Excludes measurement of net asset value as estimate of fair value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 6A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=66048111&loc=SL6742756-110258 + 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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- Definition Estimate remaining period the underlying assets are expected to be liquidated by the investees for investments for which net asset value per share is calculated (including by unit, membership interest, or other ownership interest unit measure), in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 6A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=66048111&loc=SL6742756-110258 + Details
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- Definition The amount of unfunded commitments for which the entity is obligated, to those certain investments for which net asset value per share is calculated (including by unit, membership interest, or other equity (ownership interest) unit measure) (alternative investments). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 6A -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=66048111&loc=SL6742756-110258 + Details
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