Medical Claims Payable (Reconciliation Of The Beginning And Ending Balances For Medical Claims Payable By Segment) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Medical Claims Payable [Line Items]
Gross medical claims payable, beginning of period			$ 7,892.6	$ 7,569.8
Ceded medical claims payable, beginning of period			(539.1)	(645.6)
Net medical claims payable, beginning of period			7,353.5	6,924.2
Current period net incurred medical claims			53,505.6	49,091.4
Prior periods redundancies			(1,066.3)	(772.8)
Total net incurred medical claims	$ 17,703.8	$ 16,592.7	52,439.3	48,318.6
Net payments attributable to current period medical claims			45,998.2	42,331.9
Net payments attributable to prior periods medical claims			5,932.1	5,835.5
Total net payments			51,930.3	48,167.4
Net medical claims payable, end of period	7,862.5	7,075.4	7,862.5	7,075.4
Ceded medical claims payable, end of period	101.4	397.5	101.4	397.5
Gross medical claims payable, end of period	7,963.9	7,472.9	7,963.9	7,472.9
Government Business Segment [Member]
Medical Claims Payable [Line Items]
Gross medical claims payable, beginning of period			4,625.6	4,173.7
Ceded medical claims payable, beginning of period			(17.8)	(9.9)
Net medical claims payable, beginning of period			4,607.8	4,163.8
Current period net incurred medical claims			31,634.5	28,698.7
Prior periods redundancies			(650.7)	(345.1)
Total net incurred medical claims	10,262.8	9,602.0	30,983.8	28,353.6
Net payments attributable to current period medical claims			27,274.3	24,467.9
Net payments attributable to prior periods medical claims			3,800.1	3,703.1
Total net payments			31,074.4	28,171.0
Net medical claims payable, end of period	4,517.2	4,346.4	4,517.2	4,346.4
Ceded medical claims payable, end of period	21.9	21.7	21.9	21.7
Gross medical claims payable, end of period	4,539.1	4,368.1	4,539.1	4,368.1
Commercial Specialty Business Segment [Member]
Medical Claims Payable [Line Items]
Gross medical claims payable, beginning of period			3,267.0	3,396.1
Ceded medical claims payable, beginning of period			(521.3)	(635.7)
Net medical claims payable, beginning of period			2,745.7	2,760.4
Current period net incurred medical claims			21,871.1	20,392.7
Prior periods redundancies			(415.6)	(427.7)
Total net incurred medical claims	7,441.0	6,990.7	21,455.5	19,965.0
Net payments attributable to current period medical claims			18,723.9	17,864.0
Net payments attributable to prior periods medical claims			2,132.0	2,132.4
Total net payments			20,855.9	19,996.4
Net medical claims payable, end of period	3,345.3	2,729.0	3,345.3	2,729.0
Ceded medical claims payable, end of period	79.5	375.8	79.5	375.8
Gross medical claims payable, end of period	$ 3,424.8	$ 3,104.8	$ 3,424.8	$ 3,104.8