Fair Value Measurements (Details) - USD ($) $ in Millions	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014
Assets:
Marketable debt securities	$ 5,912.4		$ 4,880.9
Fair Value, Measurements, Recurring
Assets:
Cash equivalents	874.6		909.5
Marketable equity securities	32.4		37.5
Derivative contracts	30.1		27.2
Plan assets for deferred compensation	35.6		40.1
Total	6,885.1		5,895.2
Liabilities:
Derivative contracts	24.8		14.7
Contingent consideration obligations	515.7	$ 508.3	506.0	$ 495.6	$ 461.8	$ 215.5
Total	540.5		520.7
Fair Value, Measurements, Recurring | Corporate debt securities
Assets:
Marketable debt securities	2,290.3		1,510.9
Fair Value, Measurements, Recurring | Government securities
Assets:
Marketable debt securities	2,973.4		2,875.9
Fair Value, Measurements, Recurring | Mortgage and other asset backed securities
Assets:
Marketable debt securities	648.7		494.1
Quoted Prices in Active Markets, Level 1 | Fair Value, Measurements, Recurring
Assets:
Cash equivalents	0.0		0.0
Marketable equity securities	32.4		37.5
Derivative contracts	0.0		0.0
Plan assets for deferred compensation	0.0		0.0
Total	32.4		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	874.6		909.5
Marketable equity securities	0.0		0.0
Derivative contracts	30.1		27.2
Plan assets for deferred compensation	35.6		40.1
Total	6,852.7		5,857.7
Liabilities:
Derivative contracts	24.8		14.7
Contingent consideration obligations	0.0		0.0
Total	24.8		14.7
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Corporate debt securities
Assets:
Marketable debt securities	2,290.3		1,510.9
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Government securities
Assets:
Marketable debt securities	2,973.4		2,875.9
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Mortgage and other asset backed securities
Assets:
Marketable debt securities	648.7		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	515.7		506.0
Total	515.7		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