Fair Value (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Assets:
Cash and cash equivalents	$ 3,796.0	$ 3,002.2
Short-term investments	0.4	20.6
Available-for-sale securities	1.4	4.3
Foreign currency derivatives	1.0	0.2
Cost method investments	14.4	14.2
Liabilities:
Short-term debt	11.8	28.7
Interest rate and foreign currency derivatives	39.5	48.9
Contingent purchase price obligations	215.6	386.1
Long-term debt, including current portion	5,056.9	5,035.1
Carrying Amount
Assets:
Cash and cash equivalents	3,796.0	3,002.2
Short-term investments	0.4	20.6
Available-for-sale securities	1.4	4.3
Foreign currency derivatives	1.0	0.2
Cost method investments	14.4	14.2
Liabilities:
Short-term debt	11.8	28.7
Interest rate and foreign currency derivatives	39.5	48.9
Contingent purchase price obligations	215.6	386.1
Long-term debt, including current portion	4,912.9	4,920.6
Contingent purchase price obligations
Changes in Contingent Purchase Price Obligations [Roll Forward]
January 1	386.1	322.0
Acquisitions	31.9	165.3
Revaluation and interest	(27.4)	18.0
Payments	(187.0)	(103.7)
Foreign currency translation	12.0	(15.5)
December 31	215.6	386.1
Fair Value, Measurements, Recurring [Member]
Assets:
Cash and cash equivalents	3,796.0	3,002.2
Short-term investments	0.4	20.6
Available-for-sale securities	1.4	4.3
Foreign currency derivatives	1.0	0.2
Liabilities:
Interest rate and foreign currency derivatives	39.5	48.9
Contingent purchase price obligations	215.6	386.1
Fair Value, Measurements, Recurring [Member] | Level 1
Assets:
Cash and cash equivalents	3,796.0	3,002.2
Short-term investments	0.4	20.6
Available-for-sale securities	1.4	4.3
Fair Value, Measurements, Recurring [Member] | Level 2
Assets:
Foreign currency derivatives	1.0	0.2
Liabilities:
Interest rate and foreign currency derivatives	39.5	48.9
Fair Value, Measurements, Recurring [Member] | Level 3
Liabilities:
Contingent purchase price obligations	$ 215.6	$ 386.1