Fair Value (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Assets:
Cash and cash equivalents	$ 3,652.4	$ 3,796.0
Short-term investments	5.5	0.4
Marketable equity investments	1.5	1.4
Non-marketable equity investments	11.8	14.4
Foreign currency derivatives	0.0	1.0
Liabilities:
Short-term debt	8.1	11.8
Interest rate and foreign currency derivatives	52.9	39.5
Contingent purchase price obligations	146.5	215.6
Long-term debt, including current portion	4,821.3	5,056.9
Carrying Amount
Assets:
Cash and cash equivalents	3,652.4	3,796.0
Short-term investments	5.5	0.4
Marketable equity investments	1.5	1.4
Non-marketable equity investments	11.8	14.4
Foreign currency derivatives	0.0	1.0
Liabilities:
Short-term debt	8.1	11.8
Interest rate and foreign currency derivatives	52.9	39.5
Contingent purchase price obligations	146.5	215.6
Long-term debt, including current portion	4,883.7	4,912.9
Contingent purchase price obligations
Changes in Contingent Purchase Price Obligations [Roll Forward]
January 1	215.6	386.1
Acquisitions	85.8	31.9
Revaluation and interest	(30.1)	(27.4)
Payments	(100.3)	(187.0)
Foreign currency translation	(24.5)	12.0
December 31	146.5	215.6
Fair Value, Measurements, Recurring [Member]
Assets:
Cash and cash equivalents	3,652.4	3,796.0
Short-term investments	5.5	0.4
Marketable equity investments	1.5	1.4
Foreign currency derivatives		1.0
Liabilities:
Interest rate and foreign currency derivatives	52.9	39.5
Contingent purchase price obligations	146.5	215.6
Fair Value, Measurements, Recurring [Member] | Level 1
Assets:
Cash and cash equivalents	3,652.4	3,796.0
Short-term investments	5.5	0.4
Marketable equity investments	1.5	1.4
Fair Value, Measurements, Recurring [Member] | Level 2
Assets:
Foreign currency derivatives		1.0
Liabilities:
Interest rate and foreign currency derivatives	52.9	39.5
Fair Value, Measurements, Recurring [Member] | Level 3
Liabilities:
Contingent purchase price obligations	$ 146.5	$ 215.6