Fair Value Measurements (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Assets:
Marketable debt securities	$ 5,398.0	$ 4,880.9
Fair Value, Measurements, Recurring
Assets:
Cash equivalents	2,039.6	909.5
Investments	24.9	37.5
Derivative contracts	61.0	27.2
Plan assets for deferred compensation	34.5	40.1
Total	7,558.0	5,895.2
Liabilities:
Derivative contracts	13.6	14.7
Contingent consideration obligations	467.6	506.0	$ 215.5
Total	481.2	520.7
Fair Value, Measurements, Recurring | Corporate debt securities
Assets:
Marketable debt securities	2,663.8	1,510.9
Fair Value, Measurements, Recurring | Government securities
Assets:
Marketable debt securities	2,172.5	2,875.9
Fair Value, Measurements, Recurring | Mortgage and other asset backed securities
Assets:
Marketable debt securities	561.7	494.1
Quoted Prices in Active Markets (Level 1) | Fair Value, Measurements, Recurring
Assets:
Cash equivalents	0.0	0.0
Investments	24.9	37.5
Derivative contracts	0.0	0.0
Plan assets for deferred compensation	0.0	0.0
Total	24.9	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	2,039.6	909.5
Investments	0.0	0.0
Derivative contracts	61.0	27.2
Plan assets for deferred compensation	34.5	40.1
Total	7,533.1	5,857.7
Liabilities:
Derivative contracts	13.6	14.7
Contingent consideration obligations	0.0	0.0
Total	13.6	14.7
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Corporate debt securities
Assets:
Marketable debt securities	2,663.8	1,510.9
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Government securities
Assets:
Marketable debt securities	2,172.5	2,875.9
Significant Other Observable Inputs (Level 2) | Fair Value, Measurements, Recurring | Mortgage and other asset backed securities
Assets:
Marketable debt securities	561.7	494.1
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	467.6	506.0
Total	467.6	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