Schedule 2 - Parent Company Financial Statements - Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Jul. 05, 2019	Dec. 31, 2018
ASSETS
Amortized cost of fixed maturities	$ 7,358.2	$ 6,692.7
Fixed Maturities at Fair Value (Amortized Cost: 2021 – $0.3; 2020 - $91.8)	7,986.9	7,605.9
Cost of equity securities	618.7	684.1
Equity Securities at Fair Value (Cost: 2021 - $106.8; 2020 - $73.4)	830.6	858.5
Equity Securities at Modified Cost	32.3	40.1
Cash	148.2	206.1
Other Receivables	207.3	222.4
Other Assets	592.2	575.9
Operating Lease, Right of Use Asset	64.4	68.6
Total Assets	14,916.5	14,341.9
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-term Debt, Current and Non-current, at Amortized Cost (Fair Value: 2021 - $1,152.1; 2020 - $1,247.8)	1,121.9	1,172.8
Long-term Debt, Current and Non-current	1,152.1	1,247.8
Deferred Income Tax Liabilities	227.0	285.7
Operating Lease, Liability	84.8	89.6
Accrued Expenses and Other Liabilities	843.6	727.9
Total Liabilities	10,908.8	9,778.5
Shareholders’ Equity:
Common Stock	6.4	6.5
Additional Paid-in Capital	1,790.7	1,805.2
Retained Earnings	1,762.5	2,071.2
Accumulated Other Comprehensive Income	448.1	680.5
Total Shareholders’ Equity	4,007.7	4,563.4
Total Liabilities and Shareholders’ Equity	14,916.5	14,341.9
Term Loan due July 5, 2023 (Fair Value: 2021 – $—; 2020 – $50.0) | Secured Debt
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-term Debt, Current and Non-current, at Amortized Cost (Fair Value: 2021 - $1,152.1; 2020 - $1,247.8)	0.0	49.9		$ 49.9
Senior Notes Payable, 4.35% due 2025 (Fair Value: 2021 – $481.4; 2020 – $499.5) | Senior Notes
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-term Debt, Current and Non-current, at Amortized Cost (Fair Value: 2021 - $1,152.1; 2020 - $1,247.8)	449.0	448.8
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: 2021 - $1,152.1; 2020 - $1,247.8)	396.2	395.8
Parent Company
ASSETS
Investments in Subsidiaries	4,729.1	4,896.0
Amortized cost of fixed maturities	0.3	91.8
Fixed Maturities at Fair Value (Amortized Cost: 2021 – $0.3; 2020 - $91.8)	0.4	99.8
Cost of equity securities	106.8	73.4
Equity Securities at Fair Value (Cost: 2021 - $106.8; 2020 - $73.4)	107.4	78.8
Short-term Investments at Cost which Approximates Fair Value	96.9	508.2
Cash	27.7	46.0	$ 61.8		$ 2.9
Other Receivables	2.3	1.1
Other Assets	18.9	29.2
Operating Lease, Right of Use Asset	12.8	13.4
Total Assets	4,995.5	5,672.5
LIABILITIES AND SHAREHOLDERS’ EQUITY
Current Income Tax Liability	18.5	41.5
Deferred Income Tax Liabilities	46.5	38.9
Liabilities for Benefit Plans	42.3	47.6
Operating Lease, Liability	25.8	26.9
Accrued Expenses and Other Liabilities	9.5	59.7
Total Liabilities	987.8	1,109.1
Shareholders’ Equity:
Common Stock	6.4	6.5
Additional Paid-in Capital	1,790.7	1,805.2
Retained Earnings	1,762.5	2,071.2
Accumulated Other Comprehensive Income	448.1	680.5
Total Shareholders’ Equity	4,007.7	4,563.4
Total Liabilities and Shareholders’ Equity	4,995.5	5,672.5
Parent Company | Term Loan due July 5, 2023 (Fair Value: 2021 – $—; 2020 – $50.0)
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-term Debt, Current and Non-current, at Amortized Cost (Fair Value: 2021 - $1,152.1; 2020 - $1,247.8)	0.0	49.9
Parent Company | Term Loan due July 5, 2023 (Fair Value: 2021 – $—; 2020 – $50.0) | Secured Debt
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-term Debt, Current and Non-current	0.0	50.0
Parent Company | Senior Notes Payable, 4.35% due 2025 (Fair Value: 2021 – $481.4; 2020 – $499.5)
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-term Debt, Current and Non-current, at Amortized Cost (Fair Value: 2021 - $1,152.1; 2020 - $1,247.8)	449.0	448.8
Parent Company | Senior Notes Payable, 4.35% due 2025 (Fair Value: 2021 – $481.4; 2020 – $499.5) | Senior Notes
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-term Debt, Current and Non-current	481.4	499.5
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: 2021 - $1,152.1; 2020 - $1,247.8)	396.2	395.8
Parent Company | Senior Notes, 2.400 Percent Due September 30, 2030 | Senior Notes
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-term Debt, Current and Non-current	$ 387.8	$ 405.6