Schedule II Condensed Financial Information of Registrant - Condensed Statements of Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities
Net income	$ 142.8	$ 133.3	$ 184.4
Changes in:
Other operating assets and liabilities	8.1	0.6	47.4
Other	3.0	8.0	6.4
Net cash provided by operating activities	204.9	259.8	127.6
Cash flows from investing activities
Purchase of equity securities	(46.1)	(37.4)	(15.6)
Change in short-term and other investments, net	(19.0)	12.1	(49.3)
Acquisition of businesses	0.0	0.0	(421.5)
Net cash (used in) provided by investing activities	(302.0)	(406.8)	55.9
Cash flows from financing activities
Dividends paid to shareholders	(51.4)	(49.6)	(47.3)
Proceeds from exercise of stock options	0.3	2.4	1.7
Withholding tax payments on RSUs tendered	(2.0)	(2.3)	(3.7)
Net cash provided by (used in) financing activities	208.5	143.8	(169.9)
Net increase (decrease) in cash	111.4	(3.2)	13.6
Cash at beginning of year	22.3	25.5	11.9
Cash at end of year	133.7	22.3	25.5
Parent company
Cash flows from operating activities
Net income	142.8	133.3	184.4
Equity in net earnings of subsidiaries	(162.5)	(148.7)	(205.4)
Dividends received from subsidiaries	66.0	167.0	363.2
Changes in:
Income taxes	1.8	2.0	3.4
Other operating assets and liabilities	8.4	(5.9)	8.3
Other	4.1	1.7	0.7
Net cash provided by operating activities	60.6	149.4	354.6
Cash flows from investing activities
Purchase of equity securities	0.0	1.0	0.0
Change in short-term and other investments, net	2.7	(1.5)	3.3
Capital contributions to subsidiaries	(5.0)	(97.0)	0.0
Acquisition of businesses	0.0	0.0	(444.1)
Net cash (used in) provided by investing activities	(2.3)	(97.5)	(440.8)
Cash flows from financing activities
Dividends paid to shareholders	(51.4)	(49.6)	(47.3)
Principal borrowings on Bank Credit Facility	114.0	0.0	135.0
Acquisition of treasury stock	(5.3)	(2.2)	0.0
Proceeds from exercise of stock options	0.3	2.4	1.7
Withholding tax payments on RSUs tendered	(2.0)	(2.3)	(3.7)
Net cash provided by (used in) financing activities	55.6	(51.7)	85.7
Net increase (decrease) in cash	113.9	0.2	(0.5)
Cash at beginning of year	0.3	0.1	0.6
Cash at end of year	$ 114.2	$ 0.3	$ 0.1