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Fair Value Measurements (Details) - USD ($) $ in Millions	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015
Assets:
Marketable debt securities	$ 4,356.2		$ 5,398.0
Fair Value, Measurements, Recurring
Assets:
Cash equivalents	836.0		2,039.6
Marketable equity securities	15.2		24.9
Derivative contracts	4.6		61.0
Plan assets for deferred compensation	32.9		34.5
Total	5,244.9		7,558.0
Liabilities:
Derivative contracts	70.6		13.6
Contingent consideration obligations	492.1	$ 470.9	467.6	$ 515.7	$ 508.3	$ 506.0
Total	562.7		481.2
Fair Value, Measurements, Recurring | Corporate debt securities
Assets:
Marketable debt securities	2,297.9		2,663.8
Fair Value, Measurements, Recurring | Government securities
Assets:
Marketable debt securities	1,567.8		2,172.5
Fair Value, Measurements, Recurring | Mortgage and other asset backed securities
Assets:
Marketable debt securities	490.5		561.7
Quoted Prices in Active Markets, Level 1 | Fair Value, Measurements, Recurring
Assets:
Cash equivalents	0.0		0.0
Marketable equity securities	15.2		24.9
Derivative contracts	0.0		0.0
Plan assets for deferred compensation	0.0		0.0
Total	15.2		24.9
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	836.0		2,039.6
Marketable equity securities	0.0		0.0
Derivative contracts	4.6		61.0
Plan assets for deferred compensation	32.9		34.5
Total	5,229.7		7,533.1
Liabilities:
Derivative contracts	70.6		13.6
Contingent consideration obligations	0.0		0.0
Total	70.6		13.6
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Corporate debt securities
Assets:
Marketable debt securities	2,297.9		2,663.8
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Government securities
Assets:
Marketable debt securities	1,567.8		2,172.5
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Mortgage and other asset backed securities
Assets:
Marketable debt securities	490.5		561.7
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	492.1		467.6
Total	492.1		467.6
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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