Claim and Claim Adjustment Expense Reserves (Specialty - Other Professional Liability and Management Liability - Net Incurred Claims and Allocated Claim Adjustment Expenses) (Details) - Other Professional Liability and Management Liability - Specialty $ in Millions	Dec. 31, 2025 USD ($) claim	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 10,229
IBNR	2,689
2016
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	910	$ 912	$ 906	$ 888	$ 891	$ 907	$ 904	$ 900	$ 900	$ 901
IBNR	$ 28
Cumulative Number of Claims | claim	17,993
2017
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 744	752	746	758	775	791	813	845	$ 847
IBNR	$ 25
Cumulative Number of Claims | claim	18,223
2018
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 1,003	987	941	923	906	869	864	$ 850
IBNR	$ 44
Cumulative Number of Claims | claim	20,083
2019
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 984	970	939	876	856	845	$ 837
IBNR	$ 79
Cumulative Number of Claims | claim	19,577
2020
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 936	945	945	951	944	$ 930
IBNR	$ 106
Cumulative Number of Claims | claim	19,558
2021
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 956	965	1,009	1,038	$ 1,037
IBNR	$ 190
Cumulative Number of Claims | claim	18,444
2022
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 1,049	1,084	1,112	$ 1,120
IBNR	$ 265
Cumulative Number of Claims | claim	18,534
2023
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 1,239	1,166	$ 1,149
IBNR	$ 365
Cumulative Number of Claims | claim	19,902
2024
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 1,200	$ 1,150
IBNR	$ 609
Cumulative Number of Claims | claim	20,579
2025
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 1,208
IBNR	$ 978
Cumulative Number of Claims | claim	19,311