Fair Value Measurements (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Assets:
Cash equivalents	$ 2,541.1	$ 705.5
Marketable equity securities	337.5	615.4
Derivative contracts	43.8	66.9
Plan assets for deferred compensation	27.7	25.4
Total	5,920.4	5,102.5
Liabilities:
Derivative contracts	8.3	24.6
Contingent consideration obligations	346.1	409.8	$ 523.6
Total	354.4	434.4
Corporate debt securities
Assets:
Marketable debt securities	1,695.1	2,459.2
Government securities
Assets:
Marketable debt securities	1,013.9	969.6
Mortgage and other asset backed securities
Assets:
Marketable debt securities	261.3	260.5
Quoted Prices in Active Markets (Level 1)
Assets:
Cash equivalents	0.0	0.0
Marketable equity securities	7.9	51.7
Derivative contracts	0.0	0.0
Plan assets for deferred compensation	0.0	0.0
Total	7.9	51.7
Liabilities:
Derivative contracts	0.0	0.0
Contingent consideration obligations	0.0	0.0
Total	0.0	0.0
Quoted Prices in Active Markets (Level 1) | Corporate debt securities
Assets:
Marketable debt securities	0.0	0.0
Quoted Prices in Active Markets (Level 1) | Government securities
Assets:
Marketable debt securities	0.0	0.0
Quoted Prices in Active Markets (Level 1) | Mortgage and other asset backed securities
Assets:
Marketable debt securities	0.0	0.0
Significant Other Observable Inputs (Level 2)
Assets:
Cash equivalents	2,541.1	705.5
Marketable equity securities	329.6	563.7
Derivative contracts	43.8	66.9
Plan assets for deferred compensation	27.7	25.4
Total	5,912.5	5,050.8
Liabilities:
Derivative contracts	8.3	24.6
Contingent consideration obligations	0.0	0.0
Total	8.3	24.6
Significant Other Observable Inputs (Level 2) | Corporate debt securities
Assets:
Marketable debt securities	1,695.1	2,459.2
Significant Other Observable Inputs (Level 2) | Government securities
Assets:
Marketable debt securities	1,013.9	969.6
Significant Other Observable Inputs (Level 2) | Mortgage and other asset backed securities
Assets:
Marketable debt securities	261.3	260.5
Significant Unobservable Inputs (Level 3)
Assets:
Cash equivalents	0.0	0.0
Marketable equity securities	0.0	0.0
Derivative contracts	0.0	0.0
Plan assets for deferred compensation	0.0	0.0
Total	0.0	0.0
Liabilities:
Derivative contracts	0.0	0.0
Contingent consideration obligations	346.1	409.8
Total	346.1	409.8
Significant Unobservable Inputs (Level 3) | Corporate debt securities
Assets:
Marketable debt securities	0.0	0.0
Significant Unobservable Inputs (Level 3) | Government securities
Assets:
Marketable debt securities	0.0	0.0
Significant Unobservable Inputs (Level 3) | Mortgage and other asset backed securities
Assets:
Marketable debt securities	$ 0.0	$ 0.0