Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data	Jun. 30, 2011	Dec. 31, 2010
Available-for-sale securities:
Fixed maturities, at amortized cost	$ 20,982.1	$ 20,416.5
Marketable equity securities, at cost	52.8	52.8
Trading securities:
Trading marketable equity securities, at cost	355.6	168.0
Investments in limited partnerships at fair value	$ 30.4	$ 36.5
LIABILITIES AND STOCKHOLDERS' EQUITY
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	750,000,000	750,000,000
Common stock, shares issued	118,570,964	118,216,470
Common stock, shares outstanding	118,570,964	118,216,470