Unaudited Condensed Consolidated Balance Sheets (Parenthetical) $ in Millions	Jun. 30, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares
Fixed maturity investments trading, amortized cost | $	$ 7,769.0	$ 7,290.6
Equity securities trading, cost | $	$ 205.3	$ 395.3
Common stock, shares issued	93,586,418	95,523,230
Common stock, shares outstanding	87,463,950	90,959,635
Treasury stock (shares)	6,122,468	4,563,595