Income Taxes (Narrative) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Contingency [Line Items]
Valuation Allowance Deferred Tax Asset Release	$ 6.1	$ 11.0
Valuation Allowance Deferred Tax Asset Increase	12.1	18.1
Valuation Allowance, Deferred Tax Asset, Net Change in Amount	6.0
Unrecognized tax benefits that would impact effective tax rate	61.7
Unrecognized tax benefits that would impact additional paid in capital	10.9
Unrecognized tax benefits that would impact goodwill	5.7
Tax positions for which ultimate deductibility is highly certain	0.8
Interest recognized	2.6	(9.0)	(0.1)
Interest balance accrued	18.3	15.7
Unrecognized tax benefit change reasonably possible due to tax settlements - lower amount	8.3
Unrecognized tax benefit change reasonably possible due to tax settlements - upper amount	(84.8)
Federal tax net operating loss carry forwards	44.8
Operating loss carryforwards, expiration dates	2017 through 2024
Income Taxes Paid	1,172.0	1,188.2	1,153.9
Section 338(g) Election [Member]
Income Tax Contingency [Line Items]
Tax benefit resulting from a favorable tax election made subsequent to the Amerigroup acquisition	65.0
Income tax benefit per diluted share	$ 0.21
Internal Revenue Service (IRS) [Member]
Income Tax Contingency [Line Items]
Income tax benefit from audit settlement		200.5	39.3
Income tax benefit per diluted share		$ 0.62
State Tax Examination [Member]
Income Tax Contingency [Line Items]
Income tax benefit from audit settlement			$ 10.4