Fair Value Measurements - Quantitative Information about Level 3 Fair Value Measurements (Details) $ in Millions	Dec. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale	$ 71,032	$ 64,006
Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale	3,451	3,010
Obligations of states, municipalities and political subdivisions
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale	$ 2,775	$ 3,143
Obligations of states, municipalities and political subdivisions | Minimum | Yield | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale, measurement input	0.0527	0.0509
Obligations of states, municipalities and political subdivisions | Maximum | Yield | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale, measurement input	0.0527	0.0557
Obligations of states, municipalities and political subdivisions | Weighted-average | Yield | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale, measurement input	0.0527	0.0533
Obligations of states, municipalities and political subdivisions | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale	$ 4	$ 3
Obligations of states, municipalities and political subdivisions | Level 3 | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale	2	3
Corporate debt
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale	37,235	$ 31,826
Corporate debt | Minimum | Yield | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale, measurement input		0.0683
Corporate debt | Maximum | Yield | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale, measurement input		0.1161
Corporate debt | Weighted-average | Yield | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale, measurement input		0.0922
Corporate debt | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale	113	$ 240
Corporate debt | Level 3 | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale		177
RMBS
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale	$ 10,168	$ 8,604
RMBS | Minimum | Yield | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale, measurement input	0.0525	0.0589
RMBS | Minimum | Constant prepayment rate | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale, measurement input	0.0409	0.0410
RMBS | Minimum | Loss severity | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale, measurement input	0.3929	0.4081
RMBS | Minimum | Constant default rate | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale, measurement input	0.0051	0.0057
RMBS | Maximum | Yield | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale, measurement input	0.0630	0.0698
RMBS | Maximum | Constant prepayment rate | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale, measurement input	0.0747	0.0926
RMBS | Maximum | Loss severity | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale, measurement input	0.7956	0.7672
RMBS | Maximum | Constant default rate | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale, measurement input	0.0194	0.0248
RMBS | Weighted-average | Yield | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale, measurement input	0.0577	0.0644
RMBS | Weighted-average | Constant prepayment rate | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale, measurement input	0.0578	0.0668
RMBS | Weighted-average | Loss severity | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale, measurement input	0.5942	0.5876
RMBS | Weighted-average | Constant default rate | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale, measurement input	0.0122	0.0152
RMBS | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale	$ 1,546	$ 1,894
RMBS | Level 3 | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale	$ 1,165	$ 1,321
CLO/ABS | Minimum | Yield | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale, measurement input	0.0007	0.0424
CLO/ABS | Maximum | Yield | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale, measurement input	0.1326	0.0842
CLO/ABS | Weighted-average | Yield | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale, measurement input	0.0648	0.0633
CLO/ABS | Level 3 | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale	$ 1,321	$ 760
CMBS
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale	$ 4,616	$ 3,926
CMBS | Minimum | Yield | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale, measurement input	0.0495	0.0704
CMBS | Maximum | Yield | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale, measurement input	0.0495	0.1012
CMBS | Weighted-average | Yield | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale, measurement input	0.0495	0.0870
CMBS | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale	$ 24	$ 26
CMBS | Level 3 | Discounted cash flow
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale	$ 24	$ 25