Investing Activities Gain (Loss) on Investments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Jun. 30, 2013	Sep. 30, 2013	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Investments, Debt and Equity Securities [Abstract]
Total other-than-temporary debt impairments							$ (1.1)		$ (5.0)		$ (9.7)
Portion of loss recognized in OCI	0	0	(0.2)	(0.7)	(0.9)	(0.9)	(0.9)		2.2		6.9
Net debt impairments recognized in earnings							(2.0)		(2.8)		(2.8)
Debt security impairments:
U.S. government and agency							0		0		0
State and political subdivision							0		(0.1)		0
Foreign government							0		0		0
Corporate							0		0		(0.4)
CMBS							(0.3)		(0.1)		(0.4)
RMBS							(1.5)		(1.9)		(1.5)
CDO/CLO							(0.2)		(0.4)		(0.4)
Other asset-backed							0		(0.3)		(0.1)
Net debt security impairments							(2.0)		(2.8)		(2.8)
Equity security impairments							0		0		(0.4)
Net OTTI losses recognized in earnings	(0.6)	(0.2)	(0.2)	(1.0)	(1.2)	(1.4)	(2.0)		(2.8)		(3.2)
Debt security transaction gains							11.3		22.8		2.5
Debt security transaction losses							(0.4)		(0.7)		(0.7)
Limited partnerships and other investment gains							0		0		0.1
Limited partnerships and other investment losses							0		(0.3)		(0.1)
Net transaction gains (losses)							10.9		21.8		1.8
Derivative instruments							(23.1)		(49.0)		6.2
Embedded derivatives							17.6	[1]	11.2	[1]	(33.2)	[1]
Related party reinsurance derivatives							0		(3.5)		9.0
Assets valued at fair value							0		0		0
Net realized investment losses, excluding impairment losses	13.5	(2.6)	10.9	(16.4)	(5.5)	(8.1)	5.4		(19.5)		(16.2)
Net realized investment losses, including impairment losses							$ 3.4		$ (22.3)		$ (19.4)

[1] Includes the change in fair value of embedded derivatives associated with fixed index annuity indexed crediting feature and variable annuity GMWB, GMAB and COMBO riders. See Note 7 to these financial statements for additional disclosures.