Fair Value Measurements (Details) - USD ($) $ in Millions	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Assets:
Marketable debt securities	$ 2,381.6		$ 2,051.0
Fair Value, Measurements, Recurring
Assets:
Cash equivalents	978.9		626.9
Marketable equity securities	1,166.2		1,974.3
Derivative contracts	80.0		20.5
Plan assets for deferred compensation	33.7		28.2
Total	4,640.4		4,700.9
Liabilities:
Derivative contracts	27.7		217.2
Contingent consideration obligations	210.7	$ 226.3	259.8	$ 322.6	$ 351.6	$ 346.1
Total	238.4		477.0
Fair Value, Measurements, Recurring | Corporate debt securities
Assets:
Marketable debt securities	1,486.8		1,301.5
Fair Value, Measurements, Recurring | Government securities
Assets:
Marketable debt securities	712.9		627.1
Fair Value, Measurements, Recurring | Mortgage and other asset backed securities
Assets:
Marketable debt securities	181.9		122.4
Quoted Prices in Active Markets (Level 1) | Fair Value, Measurements, Recurring
Assets:
Cash equivalents	0.0		0.0
Marketable equity securities	215.9		271.1
Derivative contracts	0.0		0.0
Plan assets for deferred compensation	0.0		0.0
Total	215.9		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	978.9		626.9
Marketable equity securities	950.3		1,703.2
Derivative contracts	80.0		20.5
Plan assets for deferred compensation	33.7		28.2
Total	4,424.5		4,429.8
Liabilities:
Derivative contracts	27.7		217.2
Contingent consideration obligations	0.0		0.0
Total	27.7		217.2
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Corporate debt securities
Assets:
Marketable debt securities	1,486.8		1,301.5
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Government securities
Assets:
Marketable debt securities	712.9		627.1
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Mortgage and other asset backed securities
Assets:
Marketable debt securities	181.9		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	210.7		259.8
Total	210.7		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