Liabilities for Outstanding Claims, Losses and Loss Adjustment Expenses (Computation of Historical Claims on Paid and Incurred Claims Data, Net of Reinsurance) (Details)	Dec. 31, 2023
Core - Commercial Multiple Peril Line [Member]
Shortduration Insurance Contracts Historical Claims Duration [Line Items]
1	32.90%
2	23.90%
3	10.70%
4	8.90%
5	7.70%
6	4.50%
7	3.50%
8	2.20%
Core - Workers' Compensation Line [Member]
Shortduration Insurance Contracts Historical Claims Duration [Line Items]
1	22.10%
2	28.70%
3	14.80%
4	8.40%
5	4.50%
6	3.10%
7	2.20%
8	1.40%
9	0.80%
10	0.40%
Core - Commercial Automobile Line [Member]
Shortduration Insurance Contracts Historical Claims Duration [Line Items]
1	13.80%
2	18.70%
3	18.50%
4	17.70%
5	12.70%
6	8.40%
7	4.20%
Core - General Liability And Umbrella - Occurrence [Member]
Shortduration Insurance Contracts Historical Claims Duration [Line Items]
1	3.20%
2	10.10%
3	14.20%
4	17.20%
5	13.80%
6	9.30%
7	4.30%
8	10.20%
9	0.30%
10	4.90%
Specialty Property And Casualty [Member]
Shortduration Insurance Contracts Historical Claims Duration [Line Items]
1	27.80%
2	23.10%
3	9.90%
4	9.70%
5	9.20%
6	6.30%
7	4.40%
Specialty - General Liability - Claims Made [Member]
Shortduration Insurance Contracts Historical Claims Duration [Line Items]
1	12.30%
2	27.80%
3	21.70%
4	12.10%
5	7.90%
6	6.60%
7	3.20%
Personal Automobile Lines [Member]
Shortduration Insurance Contracts Historical Claims Duration [Line Items]
1	28.50%
2	28.80%
3	17.50%
4	11.20%
5	6.80%
6	3.70%
Homeowners [Member]
Shortduration Insurance Contracts Historical Claims Duration [Line Items]
1	63.60%
2	29.20%
3	4.70%
4	2.30%