Investments in Unconsolidated Affiliates (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Investments in unconsolidated affiliates
Total investments in unconsolidated affiliates	$ 275.3	$ 389.7
Symetra
Investments in unconsolidated affiliates
Total investments in unconsolidated affiliates	273.6	387.5	307.7	81.3
Symetra | Common shareholders' equity.
Investments in unconsolidated affiliates
Total investments in unconsolidated affiliates	261.0	350.4	269.2	54.0
Symetra | Warrants
Investments in unconsolidated affiliates
Total investments in unconsolidated affiliates	12.6	37.1	38.5	27.3
Pentelia Capital Management
Investments in unconsolidated affiliates
Total investments in unconsolidated affiliates	$ 1.7	$ 2.2