Medical Claims Payable (Reconciliation Of The Beginning And Ending Balances For Medical Claims Payable) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Medical Claims Payable [Line Items]
Gross medical claims payable, beginning of year	$ 7,569.8	$ 6,861.2	$ 6,127.2
Ceded medical claims payable, beginning of year	(645.6)	(767.4)	(23.4)
Net medical claims payable, beginning of year	6,924.2	6,093.8	6,103.8
Business combinations and purchase adjustments		121.8
Net incurred medical claims in current year	66,371.4	60,708.4	56,305.8
Net incurred medical claims in prior years redundancies	(850.4)	(800.2)	(541.9)
Total net incurred medical claims	65,521.0	59,908.2	55,763.9
Net payments attributable to current year medical claims	59,156.6	54,067.7	50,353.9
Net payments attributable to prior years medical claims	5,935.1	5,131.9	5,420.0
Total net payments	65,091.7	59,199.6	55,773.9
Net medical claims payable, end of year	7,353.5	6,924.2	6,093.8
Ceded medical claims payable, end of year	539.1	645.6	767.4
Gross medical claims payable, end of year	7,892.6	7,569.8	6,861.2
Commercial and Specialty Business Segment [Member]
Medical Claims Payable [Line Items]
Gross medical claims payable, beginning of year	3,396.1	3,541.4	3,129.9
Ceded medical claims payable, beginning of year	(635.7)	(762.5)	(21.7)
Net medical claims payable, beginning of year	2,760.4	2,778.9	3,108.2
Business combinations and purchase adjustments		0.0
Net incurred medical claims in current year	27,797.3	26,798.5	27,708.1
Net incurred medical claims in prior years redundancies	(466.5)	(480.3)	(239.5)
Total net incurred medical claims	27,330.8	26,318.2	27,468.6
Net payments attributable to current year medical claims	25,119.3	24,145.7	25,016.9
Net payments attributable to prior years medical claims	2,226.2	2,191.0	2,781.0
Total net payments	27,345.5	26,336.7	27,797.9
Net medical claims payable, end of year	2,745.7	2,760.4	2,778.9
Ceded medical claims payable, end of year	521.3	635.7	762.5
Gross medical claims payable, end of year	3,267.0	3,396.1	3,541.4
Government Business Segment [Member]
Medical Claims Payable [Line Items]
Gross medical claims payable, beginning of year	4,173.7	3,319.8	2,997.3
Ceded medical claims payable, beginning of year	(9.9)	(4.9)	(1.7)
Net medical claims payable, beginning of year	4,163.8	3,314.9	2,995.6
Business combinations and purchase adjustments		121.8
Net incurred medical claims in current year	38,574.1	33,909.9	28,597.7
Net incurred medical claims in prior years redundancies	(383.9)	(319.9)	(302.4)
Total net incurred medical claims	38,190.2	33,590.0	28,295.3
Net payments attributable to current year medical claims	34,037.3	29,922.0	25,337.0
Net payments attributable to prior years medical claims	3,708.9	2,940.9	2,639.0
Total net payments	37,746.2	32,862.9	27,976.0
Net medical claims payable, end of year	4,607.8	4,163.8	3,314.9
Ceded medical claims payable, end of year	17.8	9.9	4.9
Gross medical claims payable, end of year	$ 4,625.6	$ 4,173.7	$ 3,319.8