Medical Claims Payable (Reconciliation Of Net Incurred Medical Claims To Benefit Expense) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
reconciliation of net incurred medical claims to benefit expense [Line Items]
Total net incurred medical claims	$ 17,173.9	$ 15,225.2
Quality Improvement And Other Claims Expense	368.9	313.6
Benefit expense	17,542.8	15,538.8
Government Business Segment [Member]
reconciliation of net incurred medical claims to benefit expense [Line Items]
Total net incurred medical claims	10,423.8	9,144.2
Commercial Specialty Business Segment [Member]
reconciliation of net incurred medical claims to benefit expense [Line Items]
Total net incurred medical claims	$ 6,750.1	$ 6,081.0