Supplemental Unaudited Quarterly Financial Information Summarized Selected Quarterly Financial Data (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		Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Jun. 30, 2013	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 149.2	$ 130.6	$ 137.1	$ 108.8	[1]	$ 114.9	$ 130.2	$ 111.7	$ 125.6	$ 245.9	$ 376.5	$ 525.7	$ 482.4	$ 478.3
Benefits and expenses	68.0	143.2	149.4	131.1	[1]	124.8	206.5	143.3	129.3	280.5	423.7	491.7	603.9	504.6
Income tax expense (benefit)	(5.5)	2.6	(16.9)	(1.9)	[1]	(7.4)	4.3	0.5	18.8	(18.8)	(16.2)	(21.7)	16.2	(6.3)
Net income (loss)	86.7	(15.2)	4.6	(20.4)	[1]	(2.5)	(80.6)	(32.1)	(22.5)	(15.8)	(31.0)	55.7	(137.7)	(20.0)
Prior period reclassification adjustment				$ 3.2								$ 3.2

[1] Results for the quarter ended March 31, 2013 include $3.2 million of income (loss) related to out of period adjustments. Such amounts are not material to any period presented.