Claim and Claim Adjustment Expense Reserves (Specialty - Surety - Net Incurred Claims and Allocated Claim Adjustment Expenses) (Details) - Surety - 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	$ 984
IBNR	456
2016
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	43	$ 43	$ 43	$ 58	$ 64	$ 67	$ 84	$ 109	$ 124	$ 124
IBNR	$ 3
Cumulative Number of Claims | claim	5,590
2017
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 66	67	67	66	71	84	103	115	$ 120
IBNR	$ 3
Cumulative Number of Claims | claim	5,928
2018
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 58	49	51	56	62	91	108	$ 114
IBNR	$ 2
Cumulative Number of Claims | claim	6,322
2019
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 81	82	82	87	98	112	$ 119
IBNR	$ 6
Cumulative Number of Claims | claim	6,286
2020
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 67	57	67	81	119	$ 128
IBNR	$ 6
Cumulative Number of Claims | claim	4,918
2021
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 74	91	110	129	$ 137
IBNR	$ 12
Cumulative Number of Claims | claim	5,003
2022
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 118	132	158	$ 155
IBNR	$ 53
Cumulative Number of Claims | claim	5,131
2023
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 147	169	$ 175
IBNR	$ 92
Cumulative Number of Claims | claim	4,889
2024
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 167	$ 171
IBNR	$ 124
Cumulative Number of Claims | claim	4,397
2025
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 163
IBNR	$ 155
Cumulative Number of Claims | claim	3,143