Claim and Claim Adjustment Expense Reserves (Commercial - Workers' Compensation - Net Incurred Claims and Allocated Claim Adjustment Expenses) (Details) - Workers' Compensation - Commercial $ 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	$ 4,469
IBNR	1,182
2016
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	287	$ 293	$ 308	$ 331	$ 355	$ 366	$ 382	$ 396	$ 405	$ 426
IBNR	$ 40
Cumulative Number of Claims | claim	32,007
2017
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 364	383	398	399	402	400	421	432	$ 440
IBNR	$ 44
Cumulative Number of Claims | claim	33,164
2018
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 393	399	404	415	415	428	440	$ 450
IBNR	$ 57
Cumulative Number of Claims | claim	34,930
2019
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 410	416	419	436	437	449	$ 452
IBNR	$ 57
Cumulative Number of Claims | claim	34,398
2020
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 363	393	414	446	466	$ 477
IBNR	$ 74
Cumulative Number of Claims | claim	29,506
2021
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 412	421	432	454	$ 468
IBNR	$ 97
Cumulative Number of Claims | claim	30,150
2022
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 467	478	489	$ 497
IBNR	$ 108
Cumulative Number of Claims | claim	33,488
2023
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 541	551	$ 555
IBNR	$ 161
Cumulative Number of Claims | claim	37,037
2024
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 586	$ 574
IBNR	$ 196
Cumulative Number of Claims | claim	38,866
2025
Short-duration Insurance Contracts, Net Incurred Claim and Claim Adjustment Expenses [Line Items]
Incurred claims and allocated claim adjustment expense, net	$ 646
IBNR	$ 348
Cumulative Number of Claims | claim	36,112