Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash Flows From Operating Activities
Net income	$ 391.0	$ 186.2	$ 155.1
Adjustments to reconcile net income to net cash provided by operating activities:
Gain from sale of Chaucer business	(131.9)
Net loss from repayment of debt	1.9		88.3
Net realized investment losses (gains)	51.3	(23.7)	(8.6)
Net amortization and depreciation	24.6	30.1	30.7
Stock-based compensation expense	13.4	12.3	12.0
Amortization of defined benefit plan costs	9.7	14.0	9.9
Deferred income tax expense (benefit)	(23.4)	39.8	(13.2)
Change in deferred acquisition costs	(19.2)	(31.8)	(7.8)
Change in premiums receivable, net of reinsurance premiums payable	(73.9)	(29.6)	(28.2)
Change in loss, loss adjustment expense and unearned premium reserves	584.9	949.5	527.8
Change in reinsurance recoverable	(248.1)	(414.0)	(35.8)
Change in expenses and taxes payable	4.6	(0.5)	12.7
Other, net	(33.6)	(27.7)	0.5
Net cash provided by operating activities	551.3	704.6	743.4
Cash Flows From Investing Activities
Proceeds from disposals and maturities of fixed maturities	1,094.2	1,225.3	1,602.3
Proceeds from disposals of equity securities and other investments	158.4	164.9	271.1
Purchase of fixed maturities	(1,425.6)	(1,645.8)	(2,020.9)
Purchase of equity securities and other investments	(178.3)	(222.6)	(351.2)
Capital expenditures	(13.1)	(18.6)	(15.7)
Net proceeds from sale of Chaucer business	635.7
Other investing activities		(9.5)	19.0
Net cash provided by (used in) investing activities	271.3	(506.3)	(495.4)
Cash Flows From Financing Activities
Proceeds from exercise of employee stock options	14.8	23.1	16.2
Proceeds from debt borrowings, net			370.7
Change in cash collateral related to securities lending program	(19.0)	(6.7)	(6.4)
Dividends paid to shareholders	(94.3)	(86.8)	(80.4)
Repayment of debt	(11.6)		(475.4)
Repurchases of common stock	(57.7)	(37.2)	(105.6)
Other financing activities	(3.2)	(4.1)	(19.9)
Net cash used in financing activities	(171.0)	(111.7)	(300.8)
Effect of exchange rate changes on cash	(4.0)	7.2	(3.4)
Net change in cash and cash equivalents	647.6	93.8	(56.2)
Net change in cash related to discontinued operations	75.2	56.8	14.0
Cash and cash equivalents, beginning of year	297.9	147.3	189.5
Cash and cash equivalents, end of year	1,020.7	297.9	147.3
Supplemental Cash Flow Information
Interest payments	47.8	47.5	53.1
Income tax net payments	$ 57.0	$ 51.1	$ 29.7