Basis Of Presentation And Significant Accounting Policies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Basis Of Presentation And Significant Accounting Policies [Line Items]
Customer cash	$ 122.6
Securities Lending Transactions Initial Collateral Percentage Value	102.00%
Allowance for doubtful accounts, premium and self-funded receivables	$ 318.3	$ 213.6
Allowance for doubtful accounts, other receivables	301.2	142.2
Derivative liability, collateral	182.7
Derivative asset, collateral	$ 32.2
Defined Benefit Plan, Alternative Method Used to Amortize Net Gains and Losses	We determine the expected return on plan assets using the calculated value of plan assets, which recognizes changes in the fair value of plan assets in a systematic manner over three years. We apply a corridor approach to amortize unrecognized actuarial gains or losses. Under this approach, only accumulated net actuarial gains or losses in excess of 10% of the greater of the projected benefit obligation or the fair value of plan assets are amortized over the average remaining service or lifetime of the workforce as a component of net periodic benefit cost.
Reserves for future policy benefits, maximum payable period	1 year
Employee stock purchase plan, purchase price per share as a percent of closing price	95.00%
Advertising and marketing expense	$ 313.5	337.0	$ 350.9
Patient Protection Affordable Care Act Health Insurance Provider Fee, annual amount to be collected by the Government through assessments to all health insurers subject to the fee	11,300.0	8,000.0
Patient Protection Affordable Care Act Health Insurance Provider Fee, amount paid	1,207.5	$ 893.3
Patient Protection Affordable Care Act Health Insurance Provider Fee, next twelve months	11,300.0
Patient Protection Affordable Care Act Health Insurance Provider Fee, two years from current fiscal year end	$ 14,300.0
Buildings and Improvements [Member] | Minimum [Member]
Basis Of Presentation And Significant Accounting Policies [Line Items]
Property and equipment, useful life	15 years
Buildings and Improvements [Member] | Maximum [Member]
Basis Of Presentation And Significant Accounting Policies [Line Items]
Property and equipment, useful life	39 years
Data Processing Equipment and Computer Software [Member] | Minimum [Member]
Basis Of Presentation And Significant Accounting Policies [Line Items]
Property and equipment, useful life	3 years
Data Processing Equipment and Computer Software [Member] | Maximum [Member]
Basis Of Presentation And Significant Accounting Policies [Line Items]
Property and equipment, useful life	5 years
Furniture And Other Equipment [Member] | Maximum [Member]
Basis Of Presentation And Significant Accounting Policies [Line Items]
Property and equipment, useful life	7 years
Deferred Tax Asset, Current [Domain]
Basis Of Presentation And Significant Accounting Policies [Line Items]
Prior period reclassification adjustment	$ 280.4
Debt Issuance Costs, Current [Member]
Basis Of Presentation And Significant Accounting Policies [Line Items]
Prior period reclassification adjustment	0.7
Debt Issuance Costs, Long-Term [Member]
Basis Of Presentation And Significant Accounting Policies [Line Items]
Prior period reclassification adjustment	$ 107.6