Business Acquisitions and Divestitures (Narrative) (Details) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Jul. 23, 2015 USD ($) $ / shares
Business Acquisition and Divestitures [Line Items]
Measurement period adjustments, goodwill reduction									$ 0.0	$ (1.8)
Goodwill	$ 17,562.2				$ 17,082.0				17,562.2	17,082.0	$ 16,917.2
Operating revenue									78,404.8	73,021.7	70,191.4
Net loss	180.9	$ 654.8	$ 859.1	$ 865.2	506.7	$ 630.9	$ 731.1	$ 701.0	2,560.0	2,569.7	2,489.7
Income (loss) from discontinued operations, net of tax					0.0	$ 0.0	$ 0.0	$ 9.6	0.0	9.6	(144.6)
(Gain) loss on disposal from discontinued operations									0.0	(3.2)	221.8
Government Business Segment [Member]
Business Acquisition and Divestitures [Line Items]
Measurement period adjustments, goodwill reduction									0.0	(0.2)
Goodwill	5,743.3				$ 5,263.1				5,743.3	5,263.1	5,363.2
Operating revenue									40,813.0	33,796.4	30,752.6
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	22,500.0								$ 22,500.0
Bridge facility commitment letter and joinder agreement, maximum borrowing term									364 days
Term loan facility, maximum borrowing capacity	4,000.0								$ 4,000.0
Simply Healthcare [Domain] | Government Business Segment [Member]
Business Acquisition and Divestitures [Line Items]
Measurement period adjustments, goodwill reduction									14.2
Goodwill	474.7								474.7
Other intangible assets	$ 430.0								$ 430.0
One Eight Hundred Contacts [Member]
Business Acquisition and Divestitures [Line Items]
Income (loss) from discontinued operations, net of tax										$ 9.6	(144.6)
(Gain) loss on disposal from discontinued operations											221.8
Tax benefit from loss on disposal from discontinued operations											$ 57.3
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