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
	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Jun. 30, 2014	Jun. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Investments, Debt and Equity Securities [Abstract]
Total other-than-temporary debt impairments											$ 1.3	$ 0.9	$ 5.0
Portion of OTTI losses recognized in other comprehensive income (“OCI”)	0	0	0	0	0.2	0.7	0	0.9	0	0.9	0	(0.9)	2.2
Net debt impairments recognized in earnings											(1.3)	(1.8)	(2.8)
Debt security impairments:
U.S. government and agency											0	0	0
State and political subdivision											0	0	(0.1)
Foreign government											0	0	0
Corporate											(1.3)	0	0
CMBS											0	(0.3)	(0.1)
RMBS											0	(1.3)	(1.9)
CDO/CLO											0	(0.2)	(0.4)
Other asset-backed											0	0	(0.3)
Net debt security impairments											(1.3)	(1.8)	(2.8)
Equity security impairments											0	0	0
Net OTTI losses recognized in earnings	(0.5)	0	0	(0.2)	(0.2)	(0.9)	0	(1.1)	(0.5)	(1.3)	(1.3)	(1.8)	(2.8)
Debt security transaction gains											6.1	11.3	22.8
Debt security transaction losses											(2.4)	(0.4)	(0.7)
Equity security transaction gains											0	0	0
Equity security transaction losses											(0.1)	0	0
Limited partnerships and other investment gains											0	0	0
Limited partnerships and other investment losses											0	0	(0.3)
Net transaction gains (losses)											3.6	10.9	21.8
Derivative instruments											(21.9)	(23.1)	(49.0)
Embedded derivative											(45.4)	11.0	4.0
Related party reinsurance derivatives											0	0	(8.0)
Net realized investment losses, excluding impairment losses	(5.3)	(1.9)	(35.1)	(5.2)	8.8	(15.5)	(37.0)	(6.7)	(42.3)	(11.9)	(63.7)	(1.2)	(31.2)
Net realized investment losses, including impairment losses											$ (65.0)	$ (3.0)	$ (34.0)