Business Acquisitions and Divestitures (Narrative) (Details) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Jul. 23, 2015 USD ($) $ / shares	Dec. 31, 2014 USD ($)
Business Acquisition and Divestitures [Line Items]
Goodwill	$ 17,561.2	$ 17,562.2		$ 17,082.0
Government Business Segment [Member]
Business Acquisition and Divestitures [Line Items]
Goodwill	5,743.3	5,743.3		$ 5,263.1
Pending Acquisition of Cigna Corporation [Domain]
Business Acquisition and Divestitures [Line Items]
Number of countries and jurisdictions in which acquiree operates			30
Cash consideration per share amount | $ / shares			$ 103.40
Merger agreement per share consideration of acquirer stock to be exchanged for acquiree stock | $ / shares			0.5152
Merger Agreement Approximate Purchase Price Gross			$ 53,000.0
Merger Agreement Approximate Pro Forma Equity Ownership of Acquirer Shareholders			67.00%
Merger Agreement Approximate Pro Forma Equity Ownership Of Acquiree Shareholders			33.00%
Bridge facility commitment letter and joinder agreement, maximum borrowing capacity	$ 19,500.0
Bridge facility commitment letter and joinder agreement, maximum borrowing term	364 days
Term loan facility, maximum borrowing capacity	$ 4,000.0
Merger Agreement, Termination Fee	$ 1,850.0
Simply Healthcare [Domain] | Government Business Segment [Member]
Business Acquisition and Divestitures [Line Items]
Goodwill		474.7
Other intangible assets		$ 430.0
Minimum [Member] | Simply Healthcare [Domain] | Customer Relationships [Member] | Government Business Segment [Member]
Business Acquisition and Divestitures [Line Items]
Intangible assets amortization period, years		2 years
Maximum [Member] | Simply Healthcare [Domain] | Customer Relationships [Member] | Government Business Segment [Member]
Business Acquisition and Divestitures [Line Items]
Intangible assets amortization period, years		4 years