Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Available for sale:
Fixed maturity securities (amortized costs)	$ 7,967.4	$ 8,019.6
Equity securities - cost	2,472.9	2,404.9
Held to maturity securities
Fixed maturity securities (fair value)	$ 1,040.5	$ 947.4
Preferred Stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred Stock, authorized shares (in shares)	75,000,000	75,000,000
Preferred Stock, outstanding shares (in shares)	0	0
Common Stock, par value (in dollars per share)	$ 1.00	$ 1.00
Common Stock, authorized shares (in shares)	500,000,000	500,000,000
Common Stock, issued shares (in shares)	263,586,666	262,719,660
Common Class B [Member]
Held to maturity securities
Common Stock, par value (in dollars per share)	$ 1.00	$ 1.00
Common Stock, authorized shares (in shares)	100,000,000	100,000,000
Common Stock, issued shares (in shares)	0	0