Fair Value Measurements - Quantitative Information about Level 3 Fair Value Measurements (Details) $ in Millions		Jun. 30, 2024 USD ($)	Dec. 31, 2023 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale	[1]	$ 62,333	$ 65,242
Obligations of states, municipalities and political subdivisions
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale		$ 4,492	$ 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		0.0547	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		0.0528	0.0523
Obligations of states, municipalities and political subdivisions | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale		$ 4	$ 3
Corporate debt
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale		$ 30,787	$ 32,346
Corporate debt | Minimum | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0569	0.0516
Corporate debt | Maximum | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.1038	0.0962
Corporate debt | Weighted-average | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0804	0.0739
Corporate debt | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale		$ 306	$ 332
RMBS
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale		$ 5,778	$ 6,207
RMBS | Minimum | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0630	0.0618
RMBS | Minimum | Constant prepayment rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0458	0.0443
RMBS | Minimum | Loss severity
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.4173	0.4321
RMBS | Minimum | Constant default rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0077	0.0082
RMBS | Maximum | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0761	0.0742
RMBS | Maximum | Constant prepayment rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.1068	0.1030
RMBS | Maximum | Loss severity
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.7679	0.7665
RMBS | Maximum | Constant default rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0262	0.0264
RMBS | Weighted-average | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0696	0.0680
RMBS | Weighted-average | Constant prepayment rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0763	0.0736
RMBS | Weighted-average | Loss severity
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.5926	0.5993
RMBS | Weighted-average | Constant default rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0170	0.0173
RMBS | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale		$ 1,268	$ 1,341
CLO/ABS | Minimum | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0547	0.0531
CLO/ABS | Maximum | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0882	0.0856
CLO/ABS | Weighted-average | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0715	0.0694
CLO/ABS | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale		$ 1,163	$ 1,100
CMBS
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale		$ 4,287	$ 4,147
CMBS | Minimum | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.0722	0.0984
CMBS | Maximum | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.1519	0.1724
CMBS | Weighted-average | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative asset, measurement input		0.1120	0.1354
CMBS | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Bonds available for sale		$ 14	$ 22

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