Investments in Unconsolidated Affiliates (Details 4) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended							1 Months Ended	3 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Symetra	Dec. 31, 2010 Symetra	Dec. 31, 2009 Symetra	Dec. 31, 2008 Symetra	Aug. 31, 2006 Delos	Sep. 30, 2010 Delos	Dec. 31, 2010 Delos	Apr. 30, 2007 Pentelia Capital Management	Dec. 31, 2011 Pentelia Capital Management	Dec. 31, 2010 Pentelia Capital Management	Dec. 31, 2009 Pentelia Capital Management
Summarized financial information
Total investments												$ 26,171.7	$ 23,500.2
Separate account assets												795.8	881.7
Total assets												28,212.7	25,636.9
Policyholder liabilities												23,140.6	21,591.5
Long-term debt												449.2	449.0
Separate account liabilities												795.8	881.7
Total liabilities												25,078.7	23,256.3
Common shareholders equity												3,134.0	2,380.6
Symetra income statement data
Net premiums earned												540.5	473.0	470.1
Net investment income												1,270.9	1,199.4	1,113.6
Total revenues												1,999.0	1,878.5	1,714.3
Policy benefits												1,307.3	1,234.6	1,197.3
Total expenses												1,720.0	1,589.4	1,533.2
Net income												199.6	200.9	128.3
Comprehensive net income												780.6	683.1	1,018.6
Ownership interest (as a percent)												15.00%					18.00%		33.00%
Amount of investment																	32.0		1.6
Equity in earnings	(36.3)	1.5	7.9	6.7	8.3	7.9	5.3	(11.6)	(20.2)	9.9	24.3	28.2	11.1	23.9						(0.2)	0.5	0.1
Equity method investments	275.3				389.7				275.3	389.7		273.6	387.5	307.7	81.3					1.7	2.2
Sale of investments																138.8		21.7
Pre-tax gain (loss) in other revenue																(14.0)		10.9
Pre-tax unrealized gains (losses)													$ 63.7	$ (9.0)