Accumulated Other Comprehensive Income (Loss) Reclassification out of Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized capital gains (losses)	$ (8.8)	$ (35.1)
Total before income taxes	(49.4)	(15.6)
Income tax expense (benefit)	2.8	(0.4)
Net income (loss)	(52.2)	(15.2)
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income (loss)	3.1	0.9
Accumulated Net Unrealized Investment Gain (Loss)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized capital gains (losses)	0.2	1.0
Total before income taxes	0.2	1.0
Income tax expense (benefit)	0.1	0.4
Net income (loss)	0.1	0.6
Accumulated Other-than-Temporary Impairment
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized capital gains (losses)	4.5	0.4
Total before income taxes	4.5	0.4
Income tax expense (benefit)	1.5	0.1
Net income (loss)	$ 3.0	$ 0.3