Investments - Summary of Investments (Details) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 4,079	$ 3,709
Gross unrealized gains	2	2
Gross unrealized losses	195	212
Estimated Fair Value	3,886	3,499
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,563	2,303
Gross unrealized gains	2	2
Gross unrealized losses	111	121
Estimated Fair Value	2,454	2,184
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	911	787
Gross unrealized gains	0	0
Gross unrealized losses	56	56
Estimated Fair Value	855	731
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	338	308
Gross unrealized gains	0	0
Gross unrealized losses	17	20
Estimated Fair Value	321	288
Municipal securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	161	160
Gross unrealized gains	0	0
Gross unrealized losses	9	11
Estimated Fair Value	152	149
U.S. Treasury notes
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	72	106
Gross unrealized gains	0	0
Gross unrealized losses	0	1
Estimated Fair Value	72	105
Other
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	34	45
Gross unrealized gains	0	0
Gross unrealized losses	2	3
Estimated Fair Value	$ 32	$ 42

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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