CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Statement Of Financial Position [Abstract]
Available-for-sale cost	$ 2,760.1	$ 2,993.1
Equity securities cost	346.9	373.5
Other investments cost	377.4	294.8
Short-term investments, Cost	$ 351.6	$ 234.3
Common shares, par value	$ 1.00	$ 1.00
Common shares, shares authorized	500,000,000	500,000,000
Common shares, shares issued	34,066,889	31,384,271
Common shares, shares outstanding	34,066,889	31,384,271
Treasury shares, shares	7,558,345	6,459,613