Segment Information (Major Product Revenues) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue from External Customer [Line Items]
Reportable segments operating revenues	$ 84,194.0	$ 78,404.8	$ 73,021.7
Commercial and Specialty Business Segment [Member]
Revenue from External Customer [Line Items]
Reportable segments operating revenues	38,692.1	37,570.8	39,199.6
Commercial and Specialty Business Segment [Member] | Managed Care Products [Member]
Revenue from External Customer [Line Items]
Reportable segments operating revenues	32,369.8	31,676.9	33,755.6
Commercial and Specialty Business Segment [Member] | Managed Care Services [Member]
Revenue from External Customer [Line Items]
Reportable segments operating revenues	4,710.1	4,344.8	3,997.8
Commercial and Specialty Business Segment [Member] | Dental/Vision Products And Services [Member]
Revenue from External Customer [Line Items]
Reportable segments operating revenues	1,182.3	1,111.7	1,037.3
Commercial and Specialty Business Segment [Member] | Other Products and Services [Member]
Revenue from External Customer [Line Items]
Reportable segments operating revenues	429.9	437.4	408.9
Government Business Segment [Member]
Revenue from External Customer [Line Items]
Reportable segments operating revenues	45,477.7	40,813.0	33,796.4
Government Business Segment [Member] | Managed Care Products [Member]
Revenue from External Customer [Line Items]
Reportable segments operating revenues	45,028.5	40,307.0	33,344.6
Government Business Segment [Member] | Managed Care Services [Member]
Revenue from External Customer [Line Items]
Reportable segments operating revenues	449.2	506.0	451.8
Other [Member]
Revenue from External Customer [Line Items]
Reportable segments operating revenues	$ 24.2	$ 21.0	$ 25.7