Investments - Summary of Investments (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 4,494	$ 4,367
Gross Unrealized Gains	54	21
Gross Unrealized Losses	66	129
Estimated Fair Value	4,482	4,259
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,837	2,781
Gross Unrealized Gains	37	16
Gross Unrealized Losses	26	65
Estimated Fair Value	2,848	2,732
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	963	951
Gross Unrealized Gains	11	4
Gross Unrealized Losses	29	44
Estimated Fair Value	945	911
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	441	376
Gross Unrealized Gains	3	1
Gross Unrealized Losses	6	12
Estimated Fair Value	438	365
Municipal securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	197	172
Gross Unrealized Gains	2	0
Gross Unrealized Losses	4	6
Estimated Fair Value	195	166
U.S. Treasury notes
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	5	40
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	5	40
Other
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	51	47
Gross Unrealized Gains	1	0
Gross Unrealized Losses	1	2
Estimated Fair Value	$ 51	$ 45

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).

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