Fair Value Measurements - Quantitative Information About Unobservable Inputs (Details) - Recurring - Significant Unobservable Inputs (Level 3) $ in Millions	Sep. 30, 2025 USD ($)	Dec. 31, 2024 USD ($)
Debt securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 351
Corporate \| Securities Priced by the Company
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 312
Corporate \| Securities Priced by the Company \| Minimum \| Liquidity
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Unobservable Adjustment	0.0060
Corporate \| Securities Priced by the Company \| Maximum \| Liquidity
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Unobservable Adjustment	0.2360
Corporate \| Securities Priced by the Company \| Weighted Average \| Liquidity
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Unobservable Adjustment	0.0400
Mortgage and other asset-backed securities \| Securities Priced by the Company
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 38
Mortgage and other asset-backed securities \| Securities Priced by the Company \| Minimum \| Liquidity
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Unobservable Adjustment	0.0120
Mortgage and other asset-backed securities \| Securities Priced by the Company \| Maximum \| Liquidity
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Unobservable Adjustment	0.0500
Mortgage and other asset-backed securities \| Securities Priced by the Company \| Weighted Average \| Liquidity
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Unobservable Adjustment	0.0290
Other debt securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Fair Value	$ 1	$ 1