Investments - Summary of Investments (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 4,459	$ 4,367
Gross Unrealized Gains	9	21
Gross Unrealized Losses	121	129
Estimated Fair Value	4,347	4,259
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,852	2,781
Gross Unrealized Gains	6	16
Gross Unrealized Losses	57	65
Estimated Fair Value	2,801	2,732
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	967	951
Gross Unrealized Gains	2	4
Gross Unrealized Losses	45	44
Estimated Fair Value	924	911
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	392	376
Gross Unrealized Gains	1	1
Gross Unrealized Losses	10	12
Estimated Fair Value	383	365
Municipal securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	193	172
Gross Unrealized Gains	0	0
Gross Unrealized Losses	7	6
Estimated Fair Value	186	166
U.S. Treasury notes
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	9	40
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	9	40
Other
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	46	47
Gross Unrealized Gains	0	0
Gross Unrealized Losses	2	2
Estimated Fair Value	$ 44	$ 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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