Schedule 2 - Parent Company Financial Statements - Statements of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Cash Flows from Operating Activities:
Net (Loss) Income		$ (301.2)	$ (120.5)	$ 409.9
Adjustments to Reconcile Net (Loss) Income to Net Cash (Used in) Provided by Operating Activities:
Income (Loss) from Change in Fair Value of Equity and Convertible Securities		79.9	(114.6)	(72.1)
Net Realized Gain on Sale of Investments		(4.3)	(64.8)	(38.1)
Impairment Losses		25.8	11.0	19.5
Loss from Early Extinguishment of Debt		3.7	0.0	0.0
Other Assets and Liabilities		(11.2)	89.1	(27.8)
Net Cash (Used in) Provided by Operating Activities		(210.3)	350.7	448.0
Cash Flows from Investing Activities:
Proceeds from the Sales, Calls and Maturities of Fixed Maturities		1,295.5	1,388.9	972.4
Fixed Maturities		(1,815.8)	(1,825.4)	(1,293.3)
Equity Securities		(58.9)	(124.3)	(319.1)
Net Sales (Purchases) of Short-term Investments		6.1	687.2	(390.8)
Equity Securities		536.0	316.6	434.4
Acquisition of Business		0.0	(316.6)	0.0
Other Investments		(13.0)	(104.9)	(43.5)
Net Cash (Used in) Provided by Investing Activities		(108.4)	(118.2)	(757.0)
Cash Flows from Financing Activities:
Proceeds from Issuance of 5.875% Fixed-Rate Reset Junior Subordinated Debentures Due 2062		145.6	0.0	0.0
Repayments of Long-term Debt		(280.0)	(50.0)	0.0
Dividends Paid		(79.7)	(80.6)	(78.9)
Proceeds from Shares Issued under Employee Stock Purchase Plan		4.9	5.4	4.4
Common Stock Repurchases		0.0	(161.7)	(110.4)
Other		0.6	3.7	5.0
Net Cash Provided by (Used in) Financing Activities		382.9	(290.4)	378.3
Net increase (decrease) in cash		64.2	(57.9)	69.3
Cash, Beginning of Year		148.2
Cash, End of Year	$ 212.4	212.4	148.2
Senior Notes, 3.800 Percent Due February 23, 2032
Cash Flows from Financing Activities:
Proceeds from Issuance of 3.800% Senior Notes due February 23, 2032		396.3	0.0	0.0
Issue Fess		(1.2)	0.0	0.0
5.875% Fixed-Rate Reset Junior Subordinated Debentures due 2062
Cash Flows from Financing Activities:
Issue Fess		(0.9)	0.0	0.0
Senior Notes, 2.400 Percent Due September 30, 2030
Cash Flows from Financing Activities:
Proceeds from Issuance of 3.800% Senior Notes due February 23, 2032		0.0	0.0	396.8
Issue Fess		0.0	0.0	(1.2)
Parent Company
Cash Flows from Operating Activities:
Net (Loss) Income		(301.2)	(120.5)	409.9
Adjustments to Reconcile Net (Loss) Income to Net Cash (Used in) Provided by Operating Activities:
Equity in Net Income (Loss) of Subsidiaries		261.7	106.0	(475.4)
Cash Dividends from Subsidiaries		25.3	170.3	216.2
Income (Loss) from Change in Fair Value of Equity and Convertible Securities		14.8	(10.0)	(4.3)
Net Realized Gain on Sale of Investments		(3.0)	(10.6)	(0.1)
Settlement Costs Related to Defined Benefit Pension Plan	0.0		0.0	64.1
Impairment Losses	0.2	0.2	0.0	0.0
Other Assets and Liabilities		(48.9)	(35.3)	52.2
Net Cash (Used in) Provided by Operating Activities		(51.1)	99.9	262.6
Cash Flows from Investing Activities:
Capital Contributed to Subsidiaries		(537.8)	(36.5)	(62.0)
Proceeds from the Sales, Calls and Maturities of Fixed Maturities		0.1	181.3	2.0
Fixed Maturities		(40.3)	0.0	0.0
Equity Securities		(5.6)	(48.7)	(21.0)
Net Sales (Purchases) of Short-term Investments		138.9	411.3	(415.7)
Equity Securities		71.9	28.5	2.2
Acquisition of Business		0.0	(370.9)	0.0
Other Investments		(3.1)	0.0	0.0
Net Cash (Used in) Provided by Investing Activities		(375.9)	165.0	(494.5)
Cash Flows from Financing Activities:
Repayments of Long-term Debt		0.0	(50.0)	0.0
Dividends Paid		(79.7)	(80.6)	(78.9)
Proceeds from Shares Issued under Employee Stock Purchase Plan		4.9	5.4	4.4
Common Stock Repurchases		0.0	(161.7)	(110.4)
Other		0.6	3.7	5.4
Net Cash Provided by (Used in) Financing Activities		465.6	(283.2)	216.1
Net increase (decrease) in cash		38.6	(18.3)	(15.8)
Cash, Beginning of Year		27.7	46.0	61.8
Cash, End of Year	$ 66.3	66.3	27.7	46.0
Parent Company | Senior Notes, 3.800 Percent Due February 23, 2032
Cash Flows from Financing Activities:
Proceeds from Issuance of 3.800% Senior Notes due February 23, 2032		396.3	0.0	0.0
Issue Fess		(1.2)	0.0	0.0
Parent Company | 5.875% Fixed-Rate Reset Junior Subordinated Debentures due 2062
Cash Flows from Financing Activities:
Issue Fess		(0.9)	0.0	0.0
Proceeds from Issuance of 5.875% Fixed-Rate Reset Junior Subordinated Debentures Due 2062		145.6	0.0	0.0
Parent Company | Senior Notes, 2.400 Percent Due September 30, 2030
Cash Flows from Financing Activities:
Proceeds from Issuance of 3.800% Senior Notes due February 23, 2032		0.0	0.0	396.8
Issue Fess		$ 0.0	$ 0.0	$ (1.2)