Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Fixed maturities, available-for-sale, amortized cost	$ 1,894.0	$ 1,831.3
Equity securities, available-for-sale, cost	236.7	235.5
Other invested assets, available-for-sale, cost	54.4	50.5
Deferred policy acquisitions costs from affiliates	49.6	46.8
Losses and loss expenses payable, affiliates	504.8	494.3
Unearned premiums, affiliates	205.4	201.7
Notes payable, affiliates	15.5	15.5
Net Postretirement and Pension Benefits	(62.3)	(63.2)
Net Other Liabilities from Affiliates	(2.8)	(5.1)
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)	47,800,000	47,700,000
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	$ (63.7)	$ (65.1)
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