Fair Value Measurements (Details) - USD ($) $ in Millions	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Assets:
Marketable debt securities	$ 2,865.5		$ 2,970.3
Fair Value, Measurements, Recurring
Assets:
Cash equivalents	1,869.6		2,541.1
Marketable equity securities	527.0		337.5
Derivative contracts	59.9		43.8
Plan assets for deferred compensation	27.7		27.7
Total	5,349.7		5,920.4
Liabilities:
Derivative contracts	14.3		8.3
Contingent consideration obligations	351.6	$ 341.6	346.1	$ 401.3	$ 421.3	$ 409.8
Total	365.9		354.4
Fair Value, Measurements, Recurring | Corporate debt securities
Assets:
Marketable debt securities	1,790.2		1,695.1
Fair Value, Measurements, Recurring | Government securities
Assets:
Marketable debt securities	966.8		1,013.9
Fair Value, Measurements, Recurring | Mortgage and other asset backed securities
Assets:
Marketable debt securities	108.5		261.3
Quoted Prices in Active Markets (Level 1) | Fair Value, Measurements, Recurring
Assets:
Cash equivalents	0.0		0.0
Marketable equity securities	344.3		7.9
Derivative contracts	0.0		0.0
Plan assets for deferred compensation	0.0		0.0
Total	344.3		7.9
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	1,869.6		2,541.1
Marketable equity securities	182.7		329.6
Derivative contracts	59.9		43.8
Plan assets for deferred compensation	27.7		27.7
Total	5,005.4		5,912.5
Liabilities:
Derivative contracts	14.3		8.3
Contingent consideration obligations	0.0		0.0
Total	14.3		8.3
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Corporate debt securities
Assets:
Marketable debt securities	1,790.2		1,695.1
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Government securities
Assets:
Marketable debt securities	966.8		1,013.9
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Mortgage and other asset backed securities
Assets:
Marketable debt securities	108.5		261.3
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	351.6		346.1
Total	351.6		346.1
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