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Investments - Summary of Amortized Cost and Estimated Fair Value of Available-for-Sale Investments, Excluding VIE Investments (Detail) - USD ($) | Dec. 31, 2023 | Dec. 31, 2022
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Debt Securities, Available-for-sale [Line Items] |  |
Fixed income securities, amortized cost | $ 2,197,000,000 | $ 2,041,000,000
Gross Unrealized Gains | 40,000,000 | 31,000,000
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 71,000,000 | 106,000,000
Available-for-sale Securities | 1,710,000,000 | 1,395,000,000
Debt Securities, Available-for-sale, Allowance for Credit Loss | 3,000,000 | 0
Debt Securities, Available-for-Sale, Current | 2,162,000,000 | 1,966,000,000
Fixed Income Investments And Other Investments [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Fixed income securities, amortized cost | 1,744,000,000 | 1,469,000,000
Municipal Bonds [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Fixed income securities, amortized cost | 72,000,000 | 44,000,000
Gross Unrealized Gains | 1,000,000 | 0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 1,000,000 | 2,000,000
Available-for-sale Securities | 72,000,000 | 43,000,000
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0
Corporate Obligations [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Fixed income securities, amortized cost | 785,000,000 | 659,000,000
Gross Unrealized Gains | 4,000,000 | 1,000,000
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 44,000,000 | 63,000,000
Available-for-sale Securities | 745,000,000 | 598,000,000
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0
Debt Security, Government, Non-US [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Fixed income securities, amortized cost | 105,000,000 | 85,000,000
Gross Unrealized Gains | 1,000,000 | 0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 6,000,000 | 9,000,000
Available-for-sale Securities | 100,000,000 | 76,000,000
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0
U.S. Government Obligations [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Fixed income securities, amortized cost | 85,000,000 | 68,000,000
Gross Unrealized Gains | 1,000,000 | 0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 4,000,000 | 4,000,000
Available-for-sale Securities | 82,000,000 | 65,000,000
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0
Residential Mortgage-Backed Securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Fixed income securities, amortized cost | 239,000,000 | 230,000,000
Gross Unrealized Gains | 28,000,000 | 28,000,000
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 14,000,000 | 19,000,000
Available-for-sale Securities | 250,000,000 | 238,000,000
Debt Securities, Available-for-sale, Allowance for Credit Loss | 3,000,000 | 0
Collateralized Debt Obligations [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Fixed income securities, amortized cost | 139,000,000 | 141,000,000
Gross Unrealized Gains | 1,000,000 | 0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 1,000,000 | 4,000,000
Available-for-sale Securities | 139,000,000 | 137,000,000
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0
Asset-backed Securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Fixed income securities, amortized cost | 301,000,000 | 227,000,000
Gross Unrealized Gains | 3,000,000 | 2,000,000
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 1,000,000 | 5,000,000
Available-for-sale Securities | 303,000,000 | 224,000,000
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0
Short-term Investments [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Fixed income securities, amortized cost | 426,000,000 | 507,000,000
Gross Unrealized Gains | 0 | 0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 0 | 0
Available-for-sale Securities | 426,000,000 | 507,000,000
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0
Commercial Mortgage Backed Securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Fixed income securities, amortized cost | 19,000,000 | 15,000,000
Gross Unrealized Gains | 0 | 0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 0 | 0
Available-for-sale Securities | 19,000,000 | 0
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 |
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Available-for-sale, Debt Securities |  | 15,000,000
Collateralized Mortgage Backed Securities [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Fixed income securities, amortized cost | 19,000,000 |
Fixed Income Investments And Other Investments [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Fixed income securities, amortized cost | 2,170,000,000 | 1,977,000,000
Gross Unrealized Gains | 40,000,000 | 31,000,000
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 71,000,000 | 106,000,000
Available-for-sale Securities | 2,135,000,000 | 1,902,000,000
Debt Securities, Available-for-sale, Allowance for Credit Loss | 3,000,000 | 0
Collateral Pledged [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Gross Unrealized Gains | 0 | 0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 0 | 0
Available-for-sale Securities | 27,000,000 | 64,000,000
Collateral Pledged [Member] | Short-term Investments [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Fixed income securities, amortized cost | 27,000,000 | 64,000,000
Gross Unrealized Gains | 0 | 0
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments | 0 | 0
Available-for-sale Securities | 27,000,000 | 64,000,000
Debt Securities, Available-for-sale, Allowance for Credit Loss | 0 | 0
Asset Pledged as Collateral [Member] |  |
Debt Securities, Available-for-sale [Line Items] |  |
Fixed income securities, amortized cost | 27,000,000 | 64,000,000
Debt Securities, Available-for-sale, Allowance for Credit Loss | $ 0 | $ 0

X
- Definition Accumulated other comprehensive loss related to portion of other than temporary impairment (OTTI) due to factors other than credit losses on debt securities categorized as available-for-sale that an entity does not intend to sell and which it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis of the debt security. The amount represented by this item is net of tax, as applicable. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -Publisher FASB -URI https://asc.fasb.org//1943274/2147482790/220-10-45-14A Reference 2: http://fasb.org/us-gaap/role/ref/otherTransitionRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 9A -Publisher FASB -URI https://asc.fasb.org//1943274/2147481830/320-10-45-9A Reference 3: http://fasb.org/us-gaap/role/ref/otherTransitionRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (aaa) -Publisher FASB -URI https://asc.fasb.org//1943274/2147481800/320-10-50-2 + Details
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- Definition Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147481800/320-10-50-2 + Details
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