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Fair Value Of Financial Instruments (Realized And Unrealized Gains And Losses Included In Earnings Pertaining To Level 3 Assets And Liabilities) (Detail) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |  |
Unrealized gains (losses) on insured derivatives | $ 7 | $ 25 | $ 31
Net gains (losses) on financial instruments at fair value and foreign exchange | (38) | 52 | (17)
Net investment losses related to other-than-temporary impairments |  | (67) | (5)
Other net realized gains (losses) | 0 | 4 | 0
Variable Interest Entity Primary Beneficiary [Member] |  |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange | 108 | 105 | 25
Other net realized gains (losses) | 37 | (62) | (171)
Fair Value Inputs Level 3 [Member] | Total Gains (Losses) Included in Earnings [Member] |  |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |  |
Unrealized gains (losses) on insured derivatives | 7 | 25 | 30
Realized gains (losses) and other settlements on insured derivatives | (1) | (10) | (56)
Net gains (losses) on financial instruments at fair value and foreign exchange | (30) | (26) | 17
Net investment losses related to other-than-temporary impairments | 0 | (1) | 0
Other net realized gains (losses) | 0 | (2) | (1)
Total revenues | 77 | 39 | 15
Fair Value Inputs Level 3 [Member] | Change in Unrealized Gains (Losses) for the Period Included in Earnings for Assets and Liabilities still held [Member] |  |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |  |
Unrealized gains (losses) on insured derivatives | 0 | 25 | 30
Realized gains (losses) and other settlements on insured derivatives | 0 | 0 | 0
Net gains (losses) on financial instruments at fair value and foreign exchange | (30) | (27) | 8
Net investment losses related to other-than-temporary impairments | 0 | 0 | 0
Other net realized gains (losses) | 0 | (2) | (1)
Total revenues | 73 | 64 | 54
Fair Value Inputs Level 3 [Member] | Variable Interest Entity Primary Beneficiary [Member] | Total Gains (Losses) Included in Earnings [Member] |  |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange | 101 | 53 | 25
Fair Value Inputs Level 3 [Member] | Variable Interest Entity Primary Beneficiary [Member] | Change in Unrealized Gains (Losses) for the Period Included in Earnings for Assets and Liabilities still held [Member] |  |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |  |
Net gains (losses) on financial instruments at fair value and foreign exchange | $ 103 | $ 68 | $ 17

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- Definition Amount of gain (loss) recognized in income from asset and liability measured at fair value on recurring basis using unobservable input (level 3). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258 + Details
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- Definition The amount of other than temporary impairment (OTTI) losses on equity securities, OTTI related to credit losses on debt securities, and OTTI losses on debt securities when the entity intends to sell the securities or it is more likely than not that the entity will be required to sell the securities before recovery of its amortized cost basis. Additionally, this item includes OTTI losses recognized during the period on investments accounted for under the cost method of accounting. + References No definition available. + Details
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- Definition The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585 + Details
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