Condensed Consolidated Balance Sheets Parenthetical (USD $) In Millions, except Share data, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Statement of Financial Position [Abstract]
Fixed maturities, available-for-sale, amortized cost	$ 65,607.9	$ 65,033.8
Equity securities, available-for-sale, cost	244.8	267.4
Mortgage loans on real estate, valuation allowance	3.4	3.8
Securities pledged amortized cost	$ 1,230.3	$ 1,457.9
Common stock, shares authorized	900,000,000	900,000,000
Common stock, shares issued	262,625,547	261,754,931
Common stock, shares outstanding	254,734,166	261,675,811
Treasury stock, shares	7,891,381	79,120
Common stock, par value	$ 0.01	$ 0.01