Fair Value Measurements (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Assets:
Marketable debt securities	$ 2,141.9	$ 2,051.0
Fair Value, Measurements, Recurring
Assets:
Cash equivalents	745.8	626.9
Marketable equity securities	1,442.8	1,974.3
Derivative contracts	51.2	20.5
Plan assets for deferred compensation	31.1	28.2
Total	4,412.8	4,700.9
Liabilities:
Derivative contracts	88.6	217.2
Contingent consideration obligations	226.0	259.8	$ 341.5	$ 346.1
Total	314.6	477.0
Fair Value, Measurements, Recurring | Corporate debt securities
Assets:
Marketable debt securities	1,336.2	1,301.5
Fair Value, Measurements, Recurring | Government securities
Assets:
Marketable debt securities	677.4	627.1
Fair Value, Measurements, Recurring | Mortgage and other asset backed securities
Assets:
Marketable debt securities	128.3	122.4
Quoted Prices in Active Markets (Level 1) | Fair Value, Measurements, Recurring
Assets:
Cash equivalents	0.0	0.0
Marketable equity securities	148.2	271.1
Derivative contracts	0.0	0.0
Plan assets for deferred compensation	0.0	0.0
Total	148.2	271.1
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) | Fair Value, Measurements, Recurring | Corporate debt securities
Assets:
Marketable debt securities	0.0	0.0
Quoted Prices in Active Markets (Level 1) | Fair Value, Measurements, Recurring | Government securities
Assets:
Marketable debt securities	0.0	0.0
Quoted Prices in Active Markets (Level 1) | Fair Value, Measurements, Recurring | Mortgage and other asset backed securities
Assets:
Marketable debt securities	0.0	0.0
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Assets:
Cash equivalents	745.8	626.9
Marketable equity securities	1,294.6	1,703.2
Derivative contracts	51.2	20.5
Plan assets for deferred compensation	31.1	28.2
Total	4,264.6	4,429.8
Liabilities:
Derivative contracts	88.6	217.2
Contingent consideration obligations	0.0	0.0
Total	88.6	217.2
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Corporate debt securities
Assets:
Marketable debt securities	1,336.2	1,301.5
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Government securities
Assets:
Marketable debt securities	677.4	627.1
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Mortgage and other asset backed securities
Assets:
Marketable debt securities	128.3	122.4
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
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	226.0	259.8
Total	226.0	259.8
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Corporate debt securities
Assets:
Marketable debt securities	0.0	0.0
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Government securities
Assets:
Marketable debt securities	0.0	0.0
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring | Mortgage and other asset backed securities
Assets:
Marketable debt securities	$ 0.0	$ 0.0