Medical Claims Payable (Reconciliation Of The Claims Development To The Claims Liability) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reconciliation Of The Claims Development To The Claims Liability [Line Items]
Cumulative incurred claims and allocated claim adjustment expenses, net of reinsurance	$ 187,296.9
Cumulative paid claims and allocated claim adjustment expenses, net of reinsurance	179,943.4
Net medical claims payable, end of year	7,353.5	$ 6,924.2	$ 6,093.8	$ 6,103.8
Ceded medical claims payable, end of year	539.1
Total gross medical claims payable, end of year	7,892.6	7,569.8	6,861.2	6,127.2
Commercial and Specialty Business Segment [Member]
Reconciliation Of The Claims Development To The Claims Liability [Line Items]
Cumulative incurred claims and allocated claim adjustment expenses, net of reinsurance	84,225.7
Cumulative paid claims and allocated claim adjustment expenses, net of reinsurance	81,480.0
Net medical claims payable, end of year	2,745.7	2,760.4	2,778.9	3,108.2
Ceded medical claims payable, end of year	521.3
Total gross medical claims payable, end of year	3,267.0	3,396.1	3,541.4	3,129.9
Government Business Segment [Member]
Reconciliation Of The Claims Development To The Claims Liability [Line Items]
Cumulative incurred claims and allocated claim adjustment expenses, net of reinsurance	103,071.2
Cumulative paid claims and allocated claim adjustment expenses, net of reinsurance	98,463.4
Net medical claims payable, end of year	4,607.8	4,163.8	3,314.9	2,995.6
Ceded medical claims payable, end of year	17.8
Total gross medical claims payable, end of year	$ 4,625.6	$ 4,173.7	$ 3,319.8	$ 2,997.3