Insurance Claim Reserves (Details) - Historical Claim Duration	Dec. 31, 2024
Business Insurance [Member] | General liability [Member]
Historical Claims Duration
Short-duration Insurance Contracts, Historical Claims Duration, Year One	3.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	10.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	16.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	18.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	14.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Six	11.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Seven	7.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Eight	4.80%
Short-duration Insurance Contracts, Historical Claims Duration, Year Nine	3.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Ten	2.50%
Business Insurance [Member] | Commercial property [Member]
Historical Claims Duration
Short-duration Insurance Contracts, Historical Claims Duration, Year One	51.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	33.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	7.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	2.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	0.70%
Business Insurance [Member] | Commercial multi-peril [Member]
Historical Claims Duration
Short-duration Insurance Contracts, Historical Claims Duration, Year One	35.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	23.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	10.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	8.80%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	6.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Six	4.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Seven	2.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year Eight	1.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year Nine	1.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Ten	0.80%
Business Insurance [Member] | Automobile [Member]
Historical Claims Duration
Short-duration Insurance Contracts, Historical Claims Duration, Year One	26.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	18.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	17.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	15.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	9.80%
Business Insurance [Member] | Workers' compensation [Member]
Historical Claims Duration
Short-duration Insurance Contracts, Historical Claims Duration, Year One	19.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	20.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	11.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	7.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	4.80%
Short-duration Insurance Contracts, Historical Claims Duration, Year Six	3.10%
Short-duration Insurance Contracts, Historical Claims Duration, Year Seven	2.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Eight	1.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Nine	1.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Ten	0.90%
Bond & Specialty Insurance [Member] | General liability [Member]
Historical Claims Duration
Short-duration Insurance Contracts, Historical Claims Duration, Year One	8.80%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	21.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	18.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	15.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	11.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Six	7.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Seven	6.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Eight	2.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Nine	1.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Ten	1.20%
Bond & Specialty Insurance [Member] | Fidelity and surety [Member]
Historical Claims Duration
Short-duration Insurance Contracts, Historical Claims Duration, Year One	21.80%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	23.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	10.50%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	4.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	6.90%
Personal Insurance [Member] | Automobile [Member]
Historical Claims Duration
Short-duration Insurance Contracts, Historical Claims Duration, Year One	56.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	23.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	9.80%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	5.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	2.60%
Personal Insurance [Member] | Homeowners (excluding Other) [Member]
Historical Claims Duration
Short-duration Insurance Contracts, Historical Claims Duration, Year One	67.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	26.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	3.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	1.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	0.70%
Personal Insurance [Member] | International - Canada [Member] | Property-casualty [Member]
Historical Claims Duration
Short-duration Insurance Contracts, Historical Claims Duration, Year One	44.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Two	17.70%
Short-duration Insurance Contracts, Historical Claims Duration, Year Three	8.00%
Short-duration Insurance Contracts, Historical Claims Duration, Year Four	7.40%
Short-duration Insurance Contracts, Historical Claims Duration, Year Five	6.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Six	4.60%
Short-duration Insurance Contracts, Historical Claims Duration, Year Seven	3.30%
Short-duration Insurance Contracts, Historical Claims Duration, Year Eight	1.90%
Short-duration Insurance Contracts, Historical Claims Duration, Year Nine	1.20%
Short-duration Insurance Contracts, Historical Claims Duration, Year Ten	0.90%