Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Available for sale:
Fixed maturity securities (amortized costs)	$ 8,370.5	$ 8,285.0
Held to maturity securities
Fixed maturity securities (fair value)	1,052.1	1,034.5
Equity securities - cost	$ 3,041.4	$ 3,039.1
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)	302,950,409	302,714,502
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