Fair Value Measurements (Details) - USD ($) $ in Millions	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014
Assets:
Marketable debt securities	$ 5,328.1		$ 4,880.9
Fair Value, Measurements, Recurring
Assets:
Cash equivalents	1,736.4		909.5
Marketable equity securities	29.0		37.5
Derivative contracts	20.3		27.2
Plan assets for deferred compensation	34.1		40.1
Total	7,147.9		5,895.2
Liabilities:
Derivative contracts	14.0		14.7
Contingent consideration obligations	521.6	$ 515.7	506.0	$ 481.4	$ 495.7	$ 215.5
Total	535.6		520.7
Fair Value, Measurements, Recurring | Corporate debt securities
Assets:
Marketable debt securities	2,632.1		1,510.9
Fair Value, Measurements, Recurring | Government securities
Assets:
Marketable debt securities	2,038.2		2,875.9
Fair Value, Measurements, Recurring | Mortgage and other asset backed securities
Assets:
Marketable debt securities	657.8		494.1
Quoted Prices in Active Markets, Level 1 | Fair Value, Measurements, Recurring
Assets:
Cash equivalents	0.0		0.0
Marketable equity securities	29.0		37.5
Derivative contracts	0.0		0.0
Plan assets for deferred compensation	0.0		0.0
Total	29.0		37.5
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	1,736.4		909.5
Marketable equity securities	0.0		0.0
Derivative contracts	20.3		27.2
Plan assets for deferred compensation	34.1		40.1
Total	7,118.9		5,857.7
Liabilities:
Derivative contracts	14.0		14.7
Contingent consideration obligations	0.0		0.0
Total	14.0		14.7
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Corporate debt securities
Assets:
Marketable debt securities	2,632.1		1,510.9
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Government securities
Assets:
Marketable debt securities	2,038.2		2,875.9
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Mortgage and other asset backed securities
Assets:
Marketable debt securities	657.8		494.1
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	521.6		506.0
Total	521.6		506.0
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