Schedule 2 - Parent Company Financial Statements - Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Mar. 10, 2022	Feb. 15, 2022	Dec. 31, 2021
ASSETS
Fixed Maturities at Fair Value (Amortized Cost: 2024 – $0.5; 2023 - $177.4)	$ 6,409.6	$ 6,881.9
Equity Securities at Fair Value (Cost: 2024 - $12.8; 2023 - $11.6)	218.5	225.8
Other Investments	199.5	241.9
Cash	64.4	64.1
Other Receivables	185.7	200.5
Current Income Taxes	63.4	64.5
Right-of-Use Assets	33.9	38.4
Other Assets	436.1	492.6
Total Assets	12,630.4	12,742.7	$ 13,313.6
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-Term Debt	1,391.6	1,389.2
Long-term Debt	1,278.4	1,213.4
Deferred Income Tax Liabilities	14.8	50.6
Present Value of Minimum Lease Payments	51.6	62.3
Accrued Expenses and Other Liabilities	705.2	737.7
Total Liabilities	9,846.1	10,237.7
Shareholders’ Equity:
Common Stock	6.4	6.4
Additional Paid-in Capital	1,854.9	1,845.3
Retained Earnings	1,231.6	1,014.3
Accumulated Other Comprehensive Loss	(304.5)	(360.8)
Total Shareholders’ Equity	2,788.4	2,505.2				$ (849.7)
Noncontrolling Interest	(4.1)	(0.2)
Total Shareholders’ Equity	2,784.3	2,505.0	2,670.6			3,129.7
Total Liabilities and Shareholders’ Equity	12,630.4	12,742.7
Senior Notes, 3.800 Percent Due February 23, 2032
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-Term Debt					$ 395.1
5.875% Fixed-Rate Reset Junior Subordinated Debentures due 2062
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-Term Debt				$ 144.7
Parent Company
ASSETS
Investments in Subsidiaries	3,773.8	3,594.1
Fixed Maturities at Fair Value (Amortized Cost: 2024 – $0.5; 2023 - $177.4)	0.5	174.3
Equity Securities at Fair Value (Cost: 2024 - $12.8; 2023 - $11.6)	10.9	9.9
Short-term Investments	453.8	180.2
Other Investments	22.2	18.8
Cash	2.3	1.5	$ 66.3			$ 27.7
Other Receivables	60.9	38.5
Current Income Taxes	54.3	33.9
Right-of-Use Assets	7.2	7.7
Other Assets	13.1	32.5
Total Assets	4,399.0	4,091.4
LIABILITIES AND SHAREHOLDERS’ EQUITY
Deferred Income Tax Liabilities	137.0	119.5
Liabilities for Benefit Plans	32.1	28.1
Present Value of Minimum Lease Payments	21.3	23.3
Accrued Expenses and Other Liabilities	28.6	26.3
Total Liabilities	1,610.6	1,586.4
Shareholders’ Equity:
Common Stock	6.4	6.4
Additional Paid-in Capital	1,854.9	1,845.3
Retained Earnings	1,231.6	1,014.3
Accumulated Other Comprehensive Loss	(304.5)	(360.8)
Total Shareholders’ Equity	2,788.4	2,505.2
Noncontrolling Interest	0.0	(0.2)
Total Shareholders’ Equity	2,788.4	2,505.0
Total Liabilities and Shareholders’ Equity	4,399.0	4,091.4
Parent Company | Senior Notes, 4.35 Percent Due February 15, 2025
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-Term Debt	449.9	449.6
Parent Company | Senior Notes, 2.400 Percent Due September 30, 2030
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-Term Debt	397.5	397.0
Parent Company | Senior Notes, 3.800 Percent Due February 23, 2032
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-Term Debt	396.5	396.0
Parent Company | 5.875% Fixed-Rate Reset Junior Subordinated Debentures due 2062
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-Term Debt	$ 147.7	$ 146.6