Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Fixed maturities, available-for-sale, amortized cost	$ 2,149.5	$ 2,095.9
Equity securities, available-for-sale, cost	297.1	323.1
Other invested assets, available-for-sale, cost	25.6	25.5
Deferred policy acquisitions costs from affiliates	40.7	50.7
Losses and loss expenses payable, affiliates	723.5	630.9
Unearned premiums, affiliates	217.0	220.9
Notes payable, affiliates	15.2	15.2
Net Postretirement and Pension Benefits	(34.5)	(40.1)
Net Other Liabilities from Affiliates	$ 18.8	$ 11.0
Common stock, no par value (usd per share)	$ 0	$ 0
Common stock, shares authorized (shares)	100,000,000	100,000,000
Common stock, shares issued (shares)	49,000,000	48,600,000
Common stock, stated value per share (usd per share)	$ 2.5	$ 2.5
Treasury stock (shares)	6,800,000	6,800,000
Net Accumulated Other Comprehensive Income	$ (51.0)	$ (53.7)
Class A Preferred Stock [Member]
Preferred stock, no par value (usd per share)	$ 0	$ 0
Preferred stock, shares authorized (shares)	2,500,000	2,500,000
Preferred stock, shares issued (shares)	0	0
Class B Preferred Stock [Member]
Preferred stock, no par value (usd per share)	$ 0	$ 0
Preferred stock, shares authorized (shares)	2,500,000	2,500,000
Preferred stock, shares issued (shares)	0	0