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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, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |  |
Unrealized gains (losses) on insured derivatives | $ 31 | $ 0 | $ 21
Net gains (losses) on financial instruments at fair value and foreign exchange | (17) | (24) | 84
Other net realized gains (losses) | 0 | 31 | (282)
Net investment losses related to other-than-temporary impairments | (5) | (106) | (5)
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 | 30 | 1 | 21
Realized gains and other settlements on insured derivatives | (56) | (51) | (43)
Net gains (losses) on financial instruments at fair value and foreign exchange | 17 | (32) | 1
Other net realized gains (losses) | (1) | 0 | 0
Net investment losses related to other-than-temporary impairments | 0 | 0 | (1)
Total revenues | 15 | 49 | (8)
Fair Value Inputs Level 3 [Member] | Change In Unrealized Gains Losses For 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 | 30 | (1) | 13
Net gains (losses) on financial instruments at fair value and foreign exchange | 8 | (32) | 1
Other net realized gains (losses) | (1) | 0 | 0
Total revenues | 54 | 98 | 46
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 | 25 | 131 | 14
Fair Value Inputs Level 3 [Member] | Variable Interest Entity Primary Beneficiary [Member] | Change In Unrealized Gains Losses For 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 | $ 17 | $ 131 | $ 32

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- Definition Amount of realized and unrealized gain (loss) included in earnings, which have arisen from the use of significant unobservable inputs (level 3) to measure fair value of assets, liabilities, and financial instruments classified in shareholders' equity. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=99377789&loc=d3e19207-110258 + 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=109223946&loc=d3e3602-108585 + Details
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