Fair Value Measurements (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Assets:
Marketable debt securities	$ 4,880.9	$ 2,111.1
Fair Value, Measurements, Recurring
Assets:
Cash equivalents	909.5	716.3
Investments	37.5	6.9
Derivative contracts	27.2	72.7
Plan assets for deferred compensation	40.1	36.9
Total	5,895.2	2,943.9
Liabilities:
Derivative contracts	14.7	5.4
Contingent consideration obligations	506.0	215.5	$ 280.9
Total	520.7	220.9
Fair Value, Measurements, Recurring | Corporate debt securities
Assets:
Marketable debt securities	1,510.9	1,063.0
Fair Value, Measurements, Recurring | Government securities
Assets:
Marketable debt securities	2,875.9	849.8
Fair Value, Measurements, Recurring | Mortgage and other asset backed securities
Assets:
Marketable debt securities	494.1	198.3
Quoted Prices in Active Markets (Level 1) | Fair Value, Measurements, Recurring
Assets:
Cash equivalents	0.0	0.0
Investments	37.5	6.9
Derivative contracts	0.0	0.0
Plan assets for deferred compensation	0.0	0.0
Total	37.5	6.9
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	909.5	716.3
Investments	0.0	0.0
Derivative contracts	27.2	72.7
Plan assets for deferred compensation	40.1	36.9
Total	5,857.7	2,937.0
Liabilities:
Derivative contracts	14.7	5.4
Contingent consideration obligations	0.0	0.0
Total	14.7	5.4
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Corporate debt securities
Assets:
Marketable debt securities	1,510.9	1,063.0
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Government securities
Assets:
Marketable debt securities	2,875.9	849.8
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Mortgage and other asset backed securities
Assets:
Marketable debt securities	494.1	198.3
Significant Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Assets:
Cash equivalents	0.0	0.0
Investments	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	506.0	215.5
Total	506.0	215.5
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