Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Statement of Financial Position [Abstract]
Fixed maturity securities investments, amortized cost	$ 16,826.7	$ 16,033.1
Equity securities investments, cost	1,168.5	869.9
Fixed maturity securities long-term investment, amortized cost	455.9	426.0
Equity securities long-term investments, cost	$ 27.4	$ 27.1
Preferred stock, par value	$ 0	$ 0
Preferred stock, shares authorized	100,000,000	100,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	900,000,000	900,000,000
Common stock, shares issued	293,273,830	304,715,144
Common stock, shares outstanding	293,273,830	304,715,144