Unaudited Condensed Consolidated Balance Sheets (Parenthetical) $ in Millions	Sep. 30, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares
Fixed maturity investments trading, amortized cost | $	$ 7,311.5	$ 7,290.6
Equity securities trading - cost | $	$ 208.0	$ 395.3
Common stock, shares issued	93,586,418	95,523,230
Common stock, shares outstanding	86,974,284	90,959,635
Treasury stock (shares)	6,612,134	4,563,595