Schedule II Condensed Financial Information of Registrant - Condensed Statements of Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Cash flows from operating activities
Net income (loss)	$ (2.6)	$ 142.8	$ 133.3
Changes in:
Other operating assets and liabilities	(28.1)	8.9	(1.0)
Net cash provided by operating activities	171.5	204.9	259.8
Cash flows from investing activities
Purchase of equity securities	(5.2)	(46.1)	(37.4)
Change in short-term and other investments, net	30.4	(19.0)	12.1
Acquisition of business, net of cash acquired	(164.4)	0.0	0.0
Net cash used in investing activities	(214.6)	(302.0)	(406.8)
Cash flows from financing activities
Dividends paid to shareholders	(52.6)	(51.4)	(49.6)
Proceeds from exercise of stock options	0.0	0.3	2.4
Withholding tax payments on RSUs tendered	(2.4)	(2.0)	(2.3)
Net cash provided by (used in) financing activities	(47.8)	208.5	143.8
Net increase (decrease) in cash	(90.9)	111.4	(3.2)
Cash at beginning of year	133.7	22.3	25.5
Cash at end of year	42.8	133.7	22.3
Parent company
Cash flows from operating activities
Net income (loss)	(2.6)	142.8	133.3
Equity in net income of subsidiaries	(19.0)	(162.5)	(148.7)
Dividends received from subsidiaries	184.3	66.0	167.0
Changes in:
Income taxes	3.9	1.8	2.0
Other operating assets and liabilities	0.8	8.4	(5.9)
Other	(2.2)	4.1	1.7
Net cash provided by operating activities	165.2	60.6	149.4
Cash flows from investing activities
Purchase of equity securities	0.0	0.0	1.0
Change in short-term and other investments, net	(0.7)	2.7	(1.5)
Capital contributions to subsidiaries	(35.0)	(5.0)	(97.0)
Acquisition of business, net of cash acquired	(164.4)	0.0	0.0
Net cash used in investing activities	(200.1)	(2.3)	(97.5)
Cash flows from financing activities
Dividends paid to shareholders	(52.6)	(51.4)	(49.6)
Principal borrowings on Revolving Credit Facility	0.0	114.0	0.0
Acquisition of treasury stock	(24.0)	(5.3)	(2.2)
Proceeds from exercise of stock options	0.0	0.3	2.4
Withholding tax payments on RSUs tendered	(2.4)	(2.0)	(2.3)
Net cash provided by (used in) financing activities	(79.0)	55.6	(51.7)
Net increase (decrease) in cash	(113.9)	113.9	0.2
Cash at beginning of year	114.2	0.3	0.1
Cash at end of year	$ 0.3	$ 114.2	$ 0.3