Investments in Unconsolidated Affiliates (Symetra) (Details) (Symetra, USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2011	Mar. 31, 2013 Common Stock	Mar. 31, 2012 Common Stock
Investments in unconsolidated affiliates
Shares of Symetra Financial Corporation owned (in shares)	17.4
Investments in unconsolidated affiliates on conversion of warrants	9.5
Fair value of investment		$ 261.0
Estimated fair value of investment per share		$ 15
After-tax equity in losses of unconsolidated affiliates		45.9
Equity in net unrealized losses increase relating to amortization of common share impairment		136.6	2.7	3.2
Ownership interest (as a percent)	15.00%
Difference between fair value and carrying amount		195.8
Term of amortization (in years)	30 years
After tax amortization through equity in earnings	0.7
After tax amortization through equity in net unrealized losses	2.5
Pre-tax unamortized basis difference	$ 175.7
Risk free interest rate (as a percent)	0.17%
Volatility rate (as a percent)	29.10%
Expected life (in years)	1 year 3 months 29 days
Class of warrant or right fair value assumptions per strike price	$ 11.49
Share price	$ 13.41