Schedule 2 - Parent Company Financial Statements - Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022		Mar. 10, 2022	Feb. 15, 2022	Dec. 31, 2021	Dec. 31, 2020
ASSETS
Amortized cost of fixed maturities	$ 7,565.8	$ 7,811.8
Fixed Maturities at Fair Value (Amortized Cost: 2023 – $177.4; 2022 - $122.5)	6,881.9	6,894.8
Cost of equity securities	209.3	247.6
Equity Securities at Fair Value (Cost: 2023 - $11.6; 2022 - $39.3)	225.8	243.2	[1]
Other Investments	241.9	269.9	[1]
Cash	64.1	212.4	[1]
Other Receivables	200.5	262.6	[1]
Current Income Taxes	64.5	167.6	[1]
Right-of-Use Assets	38.4	45.1
Other Assets	492.6	530.0	[1]
Total Assets	12,742.7	13,313.6	[1]
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-term Debt, Current and Non-current, at Amortized Cost (Fair Value: 2023 - $1,213.4; 2022 - $1,195.1)	1,389.2	1,386.9	[2]
Long-term Debt	1,213.4	1,195.1
Deferred Income Tax Liabilities	50.6	0.0	[2]
Operating Lease, Liability	62.3	72.6
Accrued Expenses and Other Liabilities	737.7	817.3	[2]
Total Liabilities	10,237.7	10,643.0	[2]
Shareholders’ Equity:
Common Stock	6.4	6.4	[2]
Additional Paid-in Capital	1,845.3	1,812.7	[2]
Retained Earnings	1,014.3	1,366.4	[2]
Accumulated Other Comprehensive Loss	(360.8)	(514.9)	[2]
Total Shareholders’ Equity	2,505.2	2,670.6	[2]
Equity, Attributable to Noncontrolling Interest	(0.2)	0.0	[2]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	2,505.0	2,670.6	[3]
Total Liabilities and Shareholders’ Equity	12,742.7	13,313.6	[2]
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: 2023 - $1,213.4; 2022 - $1,195.1)	449.6	449.3
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: 2023 - $1,213.4; 2022 - $1,195.1)	397.0	396.6
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: 2023 - $1,213.4; 2022 - $1,195.1)				$ 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: 2023 - $1,213.4; 2022 - $1,195.1)	146.6	145.5
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: 2023 - $1,213.4; 2022 - $1,195.1)					$ 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: 2023 - $1,213.4; 2022 - $1,195.1)	396.0	395.5
Parent Company
ASSETS
Investments in Subsidiaries	3,594.1	3,849.0
Amortized cost of fixed maturities	177.4	122.5
Fixed Maturities at Fair Value (Amortized Cost: 2023 – $177.4; 2022 - $122.5)	174.3	120.0
Cost of equity securities	11.6	39.3
Equity Securities at Fair Value (Cost: 2023 - $11.6; 2022 - $39.3)	9.9	24.1
Short-term Investments	180.2	67.7
Other Investments	18.8	0.0
Cash	1.5	66.3				$ 27.7	$ 46.0
Other Receivables	38.5	5.6
Current Income Taxes	33.9	12.0
Right-of-Use Assets	7.7	12.2
Other Assets	32.5	35.6
Total Assets	4,091.4	4,192.5
LIABILITIES AND SHAREHOLDERS’ EQUITY
Current Income Tax Liability	0.0	0.0
Deferred Income Tax Liabilities	119.5	49.1
Liabilities for Benefit Plans	28.1	35.4
Operating Lease, Liability	23.3	24.4
Accrued Expenses and Other Liabilities	26.3	26.1
Total Liabilities	1,586.4	1,521.9
Shareholders’ Equity:
Common Stock	6.4	6.4
Additional Paid-in Capital	1,845.3	1,812.7
Retained Earnings	1,014.3	1,366.4
Accumulated Other Comprehensive Loss	(360.8)	(514.9)
Total Shareholders’ Equity	2,505.2	2,670.6
Equity, Attributable to Noncontrolling Interest	(0.2)	0.0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	2,505.0	2,670.6
Total Liabilities and Shareholders’ Equity	4,091.4	4,192.5
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: 2023 - $1,213.4; 2022 - $1,195.1)	449.6	449.3
Parent Company | Senior Notes, 4.35 Percent Due February 15, 2025 | Senior Notes
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-term Debt	440.8	438.5
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: 2023 - $1,213.4; 2022 - $1,195.1)	397.0	396.6
Parent Company | Senior Notes, 2.400 Percent Due September 30, 2030 | Senior Notes
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-term Debt	313.6	310.3
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: 2023 - $1,213.4; 2022 - $1,195.1)	146.6	145.5
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: 2023 - $1,213.4; 2022 - $1,195.1)	396.0	395.5
Parent Company | Senior Notes, 3.800 Percent Due February 23, 2032 | Senior Notes
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-term Debt	338.4	336.2
Parent Company | Senior Notes, 5.875 Percent Due March 15, 2062 | Junior Debt
LIABILITIES AND SHAREHOLDERS’ EQUITY
Long-term Debt	$ 120.6	$ 110.1

[1] As of January 1, 2023, the Company adopted ASU 2018-12 using the modified retrospective method applied as of the transition date of January 1, 2021. Prior period amounts in the financial statements have been recast to reflect application of the new guidance. See Note 2 to the Consolidated Financial Statements for additional information.

[2] As of January 1, 2023, the Company adopted ASU 2018-12 using the modified retrospective method applied as of the transition date of January 1, 2021. Prior period amounts in the financial statements have been recast to reflect application of the new guidance. See Note 2 to the Consolidated Financial Statements for additional information.

[3] As of January 1, 2023, the Company adopted ASU 2018-12 using the modified retrospective method applied as of the transition date of January 1, 2021. Prior period amounts in the financial statements have been recast to reflect application of the new guidance. See Note 2 to the Consolidated Financial Statements for additional information.