Investments in Unconsolidated Affiliates (Details 3) (USD $) In Millions, unless otherwise specified	3 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
Changes in carrying value of investment in Symetra
Carrying value at the beginning of the period				$ 389.7					$ 389.7
Equity in earnings of Symetra	(36.3)	1.5	7.9	6.7	8.3	7.9	5.3	(11.6)	(20.2)	9.9	24.3
Carrying value at the end of the period	275.3				389.7				275.3	389.7
Symetra
Changes in carrying value of investment in Symetra
Carrying value at the beginning of the period				387.5				307.7	387.5	307.7	81.3
Equity in earnings of Symetra									28.2	11.1	23.9
Impairment of equity in earnings of investee									(50.0)
Net unrealized gains from investee's fixed maturity portfolio									85.0	72.7	191.3
Impairment of net unrealized gains from investee's fixed maturity portfolio									(148.6)
Dividends received									(4.0)	(2.6)
Decrease (increase) in value of warrants									(24.5)	(1.4)	11.2
Carrying value at the end of the period	273.6				387.5				273.6	387.5	307.7
Tax on equity in earnings									2.3	1.4	0
Equity in net unrealized gains (losses)										63.7	(9.0)
Tax on equity in net unrealized gains (losses)									0	5.2	0
Loss from dilutive effect resulting from public offering										17.9
Gain from dilutive effect resulting from public offering										1.9
Tax on net unrealized gains from investee's fixed maturity portfolio									(6.9)	0.8	0
Loss from dilutive effect resulting from dividend and issuance of restricted shares									1.0	0.8	0
Cash dividends received on warrants									2.2
Symetra | Common shareholders' equity.
Changes in carrying value of investment in Symetra
Carrying value at the beginning of the period				350.4				269.2	350.4	269.2	54.0
Equity in earnings of Symetra									28.2	11.1	23.9
Impairment of equity in earnings of investee									(50.0)
Net unrealized gains from investee's fixed maturity portfolio									85.0	72.7	191.3
Impairment of net unrealized gains from investee's fixed maturity portfolio									(148.6)
Dividends received									(4.0)	(2.6)
Carrying value at the end of the period	261.0				350.4				261.0	350.4	269.2
Tax benefit on impairment of equity in earnings									4.1
Impairment of net unrealized gains from investee's fixed maturity portfolio									12.0
Symetra | Warrants
Changes in carrying value of investment in Symetra
Carrying value at the beginning of the period				37.1				38.5	37.1	38.5	27.3
Decrease (increase) in value of warrants									(24.5)	(1.4)	11.2
Carrying value at the end of the period	$ 12.6				$ 37.1				$ 12.6	$ 37.1	$ 38.5