Fair Value Measurements (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Assets:
Marketable debt securities	$ 5,644.5	$ 4,880.9
Fair Value, Measurements, Recurring
Assets:
Cash equivalents	820.6	909.5
Marketable equity securities	32.8	37.5
Derivative contracts	30.6	27.2
Plan assets for deferred compensation	40.4	40.1
Total	6,568.9	5,895.2
Liabilities:
Derivative contracts	46.6	14.7
Contingent consideration obligations	508.3	506.0	$ 461.8	$ 215.5
Total	554.9	520.7
Fair Value, Measurements, Recurring | Corporate debt securities
Assets:
Marketable debt securities	1,855.1	1,510.9
Fair Value, Measurements, Recurring | Government securities
Assets:
Marketable debt securities	3,279.9	2,875.9
Fair Value, Measurements, Recurring | Mortgage and other asset backed securities
Assets:
Marketable debt securities	509.5	494.1
Quoted Prices in Active Markets, Level 1 | Fair Value, Measurements, Recurring
Assets:
Cash equivalents	0.0	0.0
Marketable equity securities	32.8	37.5
Derivative contracts	0.0	0.0
Plan assets for deferred compensation	0.0	0.0
Total	32.8	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	820.6	909.5
Marketable equity securities	0.0	0.0
Derivative contracts	30.6	27.2
Plan assets for deferred compensation	40.4	40.1
Total	6,536.1	5,857.7
Liabilities:
Derivative contracts	46.6	14.7
Contingent consideration obligations	0.0	0.0
Total	46.6	14.7
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Corporate debt securities
Assets:
Marketable debt securities	1,855.1	1,510.9
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Government securities
Assets:
Marketable debt securities	3,279.9	2,875.9
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Mortgage and other asset backed securities
Assets:
Marketable debt securities	509.5	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	508.3	506.0
Total	508.3	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