Income Taxes (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Contingency [Line Items]
Valuation Allowance, Deferred Tax Asset, Net Change in Amount		$ (21.5)
Income tax expense due to non-tax deductibility of the Health Insurance Provider fee payments	$ 422.6	312.6	$ 0.0
Unrecognized tax benefits that would impact effective tax rate in future periods, if recognized	113.4
Unrecognized tax benefits that would impact additional paid-in capital in future periods, if recognized	2.4
Tax positions for which ultimate deductibility is highly certain	0.3
Interest accrued	12.3	14.1
Net interest (benefit) expense	(1.8)	(4.2)	2.6
Unrecognized tax benefit change reasonably possible due to tax settlements - upper amount	3.3
Unrecognized tax benefit change reasonably possible due to tax settlements - lower amount	(159.0)
Federal tax net operating loss carry forwards	43.9
Income Taxes Paid	1,952.1	1,659.0	1,172.0
Health Insurance Provider fee [Member]
Income Tax Contingency [Line Items]
Income tax expense due to non-tax deductibility of the Health Insurance Provider fee payments	$ 422.6	$ 312.6
Income tax (benefit) expense per diluted share	$ 1.55	$ 1.09
Adverse California Franchise Tax Ruling [Member]
Income Tax Contingency [Line Items]
Income tax expense due to non-tax deductibility of the Health Insurance Provider fee payments	$ 42.3
Income tax (benefit) expense per diluted share	$ 0.16
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) expense per diluted share			$ (0.21)
Earliest Tax Year [Member]
Income Tax Contingency [Line Items]
Operating Loss Carryforwards, Expiration Date	Jan. 01, 2017
Latest Tax Year [Member]
Income Tax Contingency [Line Items]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2034
Reduction In Statutory Income Tax Rates [Member]
Income Tax Contingency [Line Items]
Valuation Allowance, Deferred Tax Asset, Net Change in Amount		$ (9.8)
Utilization Of State Net Operating Losses [Member]
Income Tax Contingency [Line Items]
Valuation Allowance, Deferred Tax Asset, Net Change in Amount		(16.2)
Sale of 1-800 CONTACTS [Member]
Income Tax Contingency [Line Items]
Valuation Allowance, Deferred Tax Asset, Net Change in Amount		$ 4.5