Medical Claims Payable (Reconciliation Of Net Incurred Medical Claims To Benefit Expense) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Reconciliation of net incurred medical claims to benefit expense [Line Items]
Total net incurred medical claims	$ 17,703.8	$ 16,592.7	$ 52,439.3	$ 48,318.6
Quality improvement and other claims expense	399.8	329.8	1,124.3	947.9
Benefit expense	18,103.6	16,922.5	53,563.6	49,266.5
Government Business Segment [Member]
Reconciliation of net incurred medical claims to benefit expense [Line Items]
Total net incurred medical claims	10,262.8	9,602.0	30,983.8	28,353.6
Commercial Specialty Business Segment [Member]
Reconciliation of net incurred medical claims to benefit expense [Line Items]
Total net incurred medical claims	$ 7,441.0	$ 6,990.7	$ 21,455.5	$ 19,965.0