Business Acquisitions Business Acquisitions (Assets Liabilities Acquired) (Details) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2017 USD ($) shares $ / shares	Dec. 31, 2016 USD ($)	Jul. 23, 2015 USD ($)
Business Acquisition [Line Items]
Goodwill	$ 17,561.2	$ 17,561.2
Pending Acquisition of Cigna Corporation [Domain]
Business Acquisition [Line Items]
Number of countries and jurisdictions In which acquiree operates	30
Cash consideration per share | $ / 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, maximum borrowing capacity	$ 19,500.0
Bridge facility, maximum borrowing term	364 days
Term loan facility, maximum borrowing capacity	$ 4,000.0
Merger Agreement, Termination Fee	$ 1,850.0