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Fair Value Measurements (Details) - USD ($) $ in Millions	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Assets:
Marketable debt securities	$ 2,223.9		$ 2,051.0
Fair Value, Measurements, Recurring
Assets:
Cash equivalents	1,180.2		626.9
Marketable equity securities	1,593.5		1,974.3
Derivative contracts	20.8		20.5
Plan assets for deferred compensation	33.7		28.2
Total	5,052.1		4,700.9
Liabilities:
Derivative contracts	72.4		217.2
Contingent consideration obligations	226.3	$ 226.0	259.8	$ 351.6	$ 341.6	$ 346.1
Total	298.7		477.0
Fair Value, Measurements, Recurring | Corporate debt securities
Assets:
Marketable debt securities	1,382.5		1,301.5
Fair Value, Measurements, Recurring | Government securities
Assets:
Marketable debt securities	688.6		627.1
Fair Value, Measurements, Recurring | Mortgage and other asset backed securities
Assets:
Marketable debt securities	152.8		122.4
Quoted Prices in Active Markets (Level 1) | Fair Value, Measurements, Recurring
Assets:
Cash equivalents	0.0		0.0
Marketable equity securities	273.3		271.1
Derivative contracts	0.0		0.0
Plan assets for deferred compensation	0.0		0.0
Total	273.3		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	1,180.2		626.9
Marketable equity securities	1,320.2		1,703.2
Derivative contracts	20.8		20.5
Plan assets for deferred compensation	33.7		28.2
Total	4,778.8		4,429.8
Liabilities:
Derivative contracts	72.4		217.2
Contingent consideration obligations	0.0		0.0
Total	72.4		217.2
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Corporate debt securities
Assets:
Marketable debt securities	1,382.5		1,301.5
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Government securities
Assets:
Marketable debt securities	688.6		627.1
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Mortgage and other asset backed securities
Assets:
Marketable debt securities	152.8		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	226.3		259.8
Total	226.3		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

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