Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	$ (13.3)	$ 6.7
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(2.7)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), beginning balance	11.4	2.6
Accumulated Other Comprehensive Income (Loss), ending balance	(4.6)	9.3
Net Unrealized Investment Losses [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	3.1	2.6
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(0.3)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), beginning balance	(1.3)	(7.4)
Accumulated Other Comprehensive Income (Loss), ending balance	1.5	(4.8)
Portion of OTTI Losses Recognized in OCI [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(16.4)	4.1
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(2.4)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated Other Comprehensive Income (Loss), beginning balance	12.7	10.0
Accumulated Other Comprehensive Income (Loss), ending balance	$ (6.1)	$ 14.1