Schedule 2 - Parent Company Financial Statements - Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2022	Mar. 10, 2022	Feb. 15, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
ASSETS
Amortized cost of fixed maturities	$ 7,811.8			$ 7,358.2
Fixed Maturities at Fair Value (Amortized Cost: 2022 – $122.5; 2021 - $0.3)	6,894.8			7,986.9
Cost of equity securities	247.6			618.7
Equity Securities at Fair Value (Cost: 2022 - $39.3; 2021 - $106.8)	243.2			830.6
Other Investments and Securities, at Cost	38.4			32.3
Cash	212.4			148.2
Other Receivables	262.6			207.3
Current Income Taxes	167.6			173.1
Right-of-Use Assets	45.1			64.4
Other Assets	530.0			592.2
Total Assets	13,364.0			14,916.5
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-term Debt, Current and Non-current, at Amortized Cost (Fair Value: 2022 - $1,195.1; 2021 - $1,152.1)	1,386.9			1,121.9
Long-term Debt	1,195.1			1,152.1
Deferred Income Tax Liabilities	0.0			227.0
Operating Lease, Liability	72.6			84.8
Accrued Expenses and Other Liabilities	817.3			843.6
Total Liabilities	10,920.8			10,908.8
Shareholders’ Equity:
Common Stock	6.4			6.4
Additional Paid-in Capital	1,812.7			1,790.7
Retained Earnings	1,380.1			1,762.5
Accumulated Other Comprehensive (Loss) Income	(756.0)			448.1
Total Shareholders’ Equity	2,443.2			4,007.7
Total Liabilities and Shareholders’ Equity	13,364.0			14,916.5
Senior Notes, 4.35 Percent Due February 15, 2025 | Senior Notes
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-term Debt, Current and Non-current, at Amortized Cost (Fair Value: 2022 - $1,195.1; 2021 - $1,152.1)	449.3			449.0
Senior Notes, 2.400 Percent Due September 30, 2030 | Senior Notes
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-term Debt, Current and Non-current, at Amortized Cost (Fair Value: 2022 - $1,195.1; 2021 - $1,152.1)	396.6			396.2
5.875% Fixed-Rate Reset Junior Subordinated Debentures due 2062
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-term Debt, Current and Non-current, at Amortized Cost (Fair Value: 2022 - $1,195.1; 2021 - $1,152.1)		$ 144.7
5.875% Fixed-Rate Reset Junior Subordinated Debentures due 2062 | Senior Notes
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-term Debt, Current and Non-current, at Amortized Cost (Fair Value: 2022 - $1,195.1; 2021 - $1,152.1)	145.5			0.0
Senior Notes, 3.800 Percent Due February 23, 2032
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-term Debt, Current and Non-current, at Amortized Cost (Fair Value: 2022 - $1,195.1; 2021 - $1,152.1)			$ 395.1
Senior Notes, 3.800 Percent Due February 23, 2032 | Senior Notes
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-term Debt, Current and Non-current, at Amortized Cost (Fair Value: 2022 - $1,195.1; 2021 - $1,152.1)	395.5			0.0
Parent Company
ASSETS
Investments in Subsidiaries	3,621.6			4,729.1
Amortized cost of fixed maturities	122.5			0.3
Fixed Maturities at Fair Value (Amortized Cost: 2022 – $122.5; 2021 - $0.3)	120.0			0.4
Cost of equity securities	39.3			106.8
Equity Securities at Fair Value (Cost: 2022 - $39.3; 2021 - $106.8)	24.1			107.4
Short-term Investments	67.7			96.9
Cash	66.3			27.7	$ 46.0	$ 61.8
Other Receivables	5.6			2.3
Current Income Taxes	12.0			0.0
Right-of-Use Assets	12.2			12.8
Other Assets	35.6			18.9
Total Assets	3,965.1			4,995.5
LIABILITIES AND SHAREHOLDERS’ EQUITY
Current Income Tax Liability	0.0			18.5
Deferred Income Tax Liabilities	49.1			46.5
Liabilities for Benefit Plans	35.4			42.3
Operating Lease, Liability	24.4			25.8
Accrued Expenses and Other Liabilities	26.1			9.5
Total Liabilities	1,521.9			987.8
Shareholders’ Equity:
Common Stock	6.4			6.4
Additional Paid-in Capital	1,812.7			1,790.7
Retained Earnings	1,380.1			1,762.5
Accumulated Other Comprehensive (Loss) Income	(756.0)			448.1
Total Shareholders’ Equity	2,443.2			4,007.7
Total Liabilities and Shareholders’ Equity	3,965.1			4,995.5
Parent Company | Senior Notes, 4.35 Percent Due February 15, 2025
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-term Debt, Current and Non-current, at Amortized Cost (Fair Value: 2022 - $1,195.1; 2021 - $1,152.1)	449.3			449.0
Parent Company | Senior Notes, 4.35 Percent Due February 15, 2025 | Senior Notes
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-term Debt	438.5			481.4
Parent Company | Senior Notes, 2.400 Percent Due September 30, 2030
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-term Debt, Current and Non-current, at Amortized Cost (Fair Value: 2022 - $1,195.1; 2021 - $1,152.1)	396.6			396.2
Parent Company | Senior Notes, 2.400 Percent Due September 30, 2030 | Senior Notes
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-term Debt	310.3			387.8
Parent Company | 5.875% Fixed-Rate Reset Junior Subordinated Debentures due 2062
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-term Debt, Current and Non-current, at Amortized Cost (Fair Value: 2022 - $1,195.1; 2021 - $1,152.1)	145.5			0.0
Parent Company | Senior Notes, 3.800 Percent Due February 23, 2032
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-term Debt, Current and Non-current, at Amortized Cost (Fair Value: 2022 - $1,195.1; 2021 - $1,152.1)	395.5			0.0
Parent Company | Senior Notes, 3.800 Percent Due February 23, 2032 | Senior Notes
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-term Debt	336.2			0.0
Parent Company | Senior Notes, 5.875 Percent Due March 15, 2062 | Junior Debt
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-term Debt	$ 110.1			$ 0.0