Investments (Maturities of Available-for-Sale Debt Securities) (Details) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Investments
Due in one year or less, Amortized Cost	$ 164.8
Due in one year or less, Fair Value	167.3
Due after one year through five years, Amortized Cost	1,100.8
Due after one year through five years, Fair Value	1,182.8
Due after five years through ten years, Amortized Cost	1,458.8
Due after five years through ten years, Fair Value	1,544.3
Due after ten years, Amortized Cost	692.3
Due after ten years, Fair Value	706.2
Total fixed maturities, Amortized Cost	3,416.7
Total fixed maturities, Fair Value	3,600.6
Mortgage-backed and asset-backed securities, Amortized Cost	1,049.6
Mortgage-backed and asset-backed securities, Fair Value	1,097.3
Total fixed maturities, Amortized Cost	4,466.3	4,598.8
Total fixed maturities, excluding discontinued operations, Fair Value	$ 4,697.9	$ 4,797.9