Summary of Significant Accounting Policies (Health Plan Services Health Care Cost) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Health Care Organizations [Line Items]
Provision For Adverse Deviation	$ 77.7		$ 53.4
Liability for unpaid claims and claims adjustment expense, incurred claims, prior years	(14.6)	[1]	(56.2)	[1]	34.5	[1]
Prior Years Unfavorable Reserve Development	36.6
Provision For Adverse Deviation, Release	51.2
Premium deficiency reserve	$ 0		$ 0

[1] This line represents the change in reserves attributable to the difference between the original estimate of incurred claims for prior years and the revised estimate. Negative amounts in this line represent favorable development in estimated prior years’ health care costs. Positive amounts in this line represent unfavorable development in estimated prior years’ health care costs. The net favorable development related to prior years that was recorded in the year ended December 31, 2014 consisted of $36.6 million in unfavorable prior year development primarily due to unanticipated benefit utilization in our commercial business arising from dates of service in the fourth quarter of 2013 as a result of an uncertain environment related to the ACA and a release of $51.2 million of the provision for adverse deviation held at December 31, 2013. The favorable development related to prior years that was recorded in the year ended December 31, 2013 resulted from claims being settled for amounts less than originally estimated. In 2013, this was primarily due to the absence of moderately adverse conditions. The favorable developments related to prior years that were recorded in 2014 and 2013 do not directly correspond to an increase in our operating results for those periods because any favorable prior period reserve development increases current period net income only to the extent that the current period provision for adverse deviation (see footnote (f)) is less than the benefit recognized from the prior period favorable development. The unfavorable development in estimated prior years' health care costs for 2012 primarily resulted from significant delays in claims submissions for the fourth quarter of 2011 arising from issues related to a new billing format required by HIPAA combined with an unanticipated flattening of commercial trends. See Note 2 under the heading "Health Plan Services Health Care Cost" for more information.