Fair Value Measurements - Quantitative Information about Level 3 Fair Value Measurements (Details) $ in Millions		Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale	[1]	$ 64,006	$ 65,242
Obligations of states, municipalities and political subdivisions
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale		$ 3,143	$ 4,833
Obligations of states, municipalities and political subdivisions | Minimum | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0509	0.0500
Obligations of states, municipalities and political subdivisions | Maximum | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0557	0.0550
Obligations of states, municipalities and political subdivisions | Weighted-average | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0533	0.0523
Obligations of states, municipalities and political subdivisions | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale		$ 3	$ 3
Corporate debt
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale		$ 31,826	$ 32,346
Corporate debt | Minimum | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0683	0.0516
Corporate debt | Maximum | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.1161	0.0962
Corporate debt | Weighted-average | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0922	0.0739
Corporate debt | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale		$ 177	$ 332
RMBS
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale		$ 8,604	$ 6,207
RMBS | Minimum | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0589	0.0618
RMBS | Minimum | Constant prepayment rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0410	0.0443
RMBS | Minimum | Loss severity
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.4081	0.4321
RMBS | Minimum | Constant default rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0057	0.0082
RMBS | Maximum | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0698	0.0742
RMBS | Maximum | Constant prepayment rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0926	0.1030
RMBS | Maximum | Loss severity
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.7672	0.7665
RMBS | Maximum | Constant default rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0248	0.0264
RMBS | Weighted-average | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0644	0.0680
RMBS | Weighted-average | Constant prepayment rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0668	0.0736
RMBS | Weighted-average | Loss severity
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.5876	0.5993
RMBS | Weighted-average | Constant default rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0152	0.0173
RMBS | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale		$ 1,321	$ 1,341
CLO/ABS | Minimum | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0424	0.0531
CLO/ABS | Maximum | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0842	0.0856
CLO/ABS | Weighted-average | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0633	0.0694
CLO/ABS | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale		$ 760	$ 1,100
CMBS
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale		$ 3,926	$ 4,147
CMBS | Minimum | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0704	0.0984
CMBS | Maximum | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.1012	0.1724
CMBS | Weighted-average | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0870	0.1354
CMBS | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale		$ 25	$ 22

[1] See Note 10 for details of balances associated with variable interest entities.