Segment Information (Major Product Revenues) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenue from External Customer [Line Items]
Reportable segments operating revenues	$ 78,404.8	$ 73,021.7	$ 70,191.4
Commercial and Specialty Business [Member]
Revenue from External Customer [Line Items]
Reportable segments operating revenues	37,570.8	39,199.6	39,404.2
Commercial and Specialty Business [Member] | Managed Care Products [Member]
Revenue from External Customer [Line Items]
Reportable segments operating revenues	31,676.9	33,755.6	34,516.9
Commercial and Specialty Business [Member] | Managed Care Services [Member]
Revenue from External Customer [Line Items]
Reportable segments operating revenues	4,344.8	3,997.8	3,474.0
Commercial and Specialty Business [Member] | Dental/Vision Products And Services [Member]
Revenue from External Customer [Line Items]
Reportable segments operating revenues	1,111.7	1,037.3	952.5
Commercial and Specialty Business [Member] | Other Products and Services [Member]
Revenue from External Customer [Line Items]
Reportable segments operating revenues	437.4	408.9	460.8
Government Business [Member]
Revenue from External Customer [Line Items]
Reportable segments operating revenues	40,813.0	33,796.4	30,752.6
Government Business [Member] | Managed Care Products [Member]
Revenue from External Customer [Line Items]
Reportable segments operating revenues	40,307.0	33,344.6	30,347.1
Government Business [Member] | Managed Care Services [Member]
Revenue from External Customer [Line Items]
Reportable segments operating revenues	506.0	451.8	405.5
Other [Member]
Revenue from External Customer [Line Items]
Reportable segments operating revenues	$ 21.0	$ 25.7	$ 34.6