Schedule II Condensed Financial Information of Registrant - Condensed Statements of Cash Flows (Details) - USD ($) $ in Millions		3 Months Ended										12 Months Ended
		Dec. 31, 2022		Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021		Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2023		Dec. 31, 2022		Dec. 31, 2021
Cash flows from operating activities
Net income		$ (16.7)		$ 20.4	$ (4.2)	$ 20.3	$ 46.9		$ 20.2	$ 54.2	$ 49.1	$ 45.0		$ 19.8	[1],[2]	$ 170.4	[1],[2]
Changes in:
Other operating assets and liabilities												53.9		(109.4)	[2]	4.5	[2]
Net cash provided by operating activities												302.1		171.5	[2]	204.9	[2]
Cash flows from investing activities
Purchase of equity securities												(2.5)		(5.2)	[2]	(46.1)	[2]
Other, net												9.2		(9.6)		(10.2)
Acquisition of business, net of cash acquired												0.0		(164.4)	[2]	0.0	[2]
Net cash used in investing activities												(107.4)		(214.6)	[2]	(302.0)	[2]
Cash flows from financing activities
Dividends paid to shareholders												(53.9)		(52.6)	[2]	(51.4)	[2]
Proceeds from issuance of 2023 Senior Notes due 2028												297.7		0.0	[2]	0.0	[2]
Principal repayment on Revolving Credit Facility												(249.0)		0.0		0.0
Proceeds from exercise of stock options												0.0		0.0		0.3
Withholding tax payments on RSUs tendered												(1.8)		(2.4)	[2]	(2.0)	[2]
Net cash provided by (used in) financing activities												(207.8)		(47.8)	[2]	208.5	[2]
Net increase (decrease) in cash												(13.1)		(90.9)	[2]	111.4	[2]
Cash at beginning of year	[2]					133.7					22.3	42.8	[3]	133.7		22.3
Cash at end of year		42.8	[2],[3]				133.7	[2]				29.7		42.8	[2],[3]	133.7	[2]
Parent company
Cash flows from operating activities
Net income												45.0		19.8		170.4
Equity in net income of subsidiaries												(72.7)		(41.3)		(190.1)
Dividends received from subsidiaries												132.1		184.3		66.0
Changes in:
Income taxes												(5.8)		3.9		1.8
Other operating assets and liabilities												6.0		0.8		8.4
Other												1.2		(1.5)		(2.6)
Net cash provided by operating activities												105.8		166.0		53.9
Cash flows from investing activities
Purchase of equity securities												0.0		0.0		0.0
Other, net												(1.3)		(0.7)		2.7
Capital contributions to subsidiaries												(98.0)		(35.0)		(5.0)
Acquisition of business, net of cash acquired												0.0		(172.3)		0.0
Net cash used in investing activities												(99.3)		(208.0)		(2.3)
Cash flows from financing activities
Dividends paid to shareholders												(53.9)		(52.6)		(51.4)
Proceeds from issuance of 2023 Senior Notes due 2028												296.5		0.0		0.0
Principal borrowings on Revolving Credit Facility												0.0		0.0		114.0
Principal repayment on Revolving Credit Facility												(249.0)		0.0		0.0
Acquisition of treasury stock												(6.5)		(24.0)		(5.3)
Proceeds from exercise of stock options												0.0		0.0		0.3
Withholding tax payments on RSUs tendered												(1.8)		(2.4)		(2.0)
Proceeds for Share-based compensation												8.0		7.1		6.7
Net cash provided by (used in) financing activities												(6.7)		(71.9)		62.3
Net increase (decrease) in cash												(0.2)		(113.9)		113.9
Cash at beginning of year						$ 114.2					$ 0.3	0.3		114.2		0.3
Cash at end of year		$ 0.3					$ 114.2					$ 0.1		$ 0.3		$ 114.2

[1] Recast for the adoption of ASU 2018-12. See Note 1 of the Consolidated Financial Statements

[2] Recast for the adoption of ASU 2018-12. See Note 1 of the Consolidated Financial Statements

[3] Recast for the adoption of ASU 2018-12. See Note 1 of the Consolidated Financial Statements