Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Mar. 31, 2012	Dec. 31, 2011
Assets:
Marketable debt securities	$ 614.4		$ 3,171.7
Fair Value, Measurements, Recurring [Member]
Assets:
Cash equivalents	287.2		439.4
Derivative contracts	1.8		1.8
Plan assets for deferred compensation	21.1		14.3
Total	992.4		3,656.5
Liabilities:
Derivative contracts	17.1		14.4
Contingent consideration obligations	281.0	281.0	293.9	290.3	280.9	151.0
Total	298.1		308.3
Fair Value, Measurements, Recurring [Member] | Corporate debt securities [Member]
Assets:
Marketable debt securities	287.0		1,001.0
Fair Value, Measurements, Recurring [Member] | Government securities [Member]
Assets:
Marketable debt securities	267.2		1,657.8
Fair Value, Measurements, Recurring [Member] | Mortgage and other asset backed securities [Member]
Assets:
Marketable debt securities	60.2		512.9
Fair Value, Measurements, Recurring [Member] | Marketable equity securities [Member]
Assets:
Investments	40.3		9.0
Fair Value, Measurements, Recurring [Member] | Venture capital investments [Member]
Assets:
Investments	27.6	23.5	20.3	25.2	25.4	23.5
Quoted Prices in Active Markets, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Cash equivalents	0		0
Derivative contracts	0		0
Plan assets for deferred compensation	0		0
Total	40.3		9.0
Liabilities:
Derivative contracts	0		0
Contingent consideration obligations	0		0
Total	0		0
Quoted Prices in Active Markets, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Corporate debt securities [Member]
Assets:
Marketable debt securities	0		0
Quoted Prices in Active Markets, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Government securities [Member]
Assets:
Marketable debt securities	0		0
Quoted Prices in Active Markets, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Mortgage and other asset backed securities [Member]
Assets:
Marketable debt securities	0		0
Quoted Prices in Active Markets, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Marketable equity securities [Member]
Assets:
Investments	40.3		9.0
Quoted Prices in Active Markets, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Venture capital investments [Member]
Assets:
Investments	0		0
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Cash equivalents	287.2		439.4
Derivative contracts	1.8		1.8
Plan assets for deferred compensation	21.1		14.3
Total	924.5		3,627.2
Liabilities:
Derivative contracts	17.1		14.4
Contingent consideration obligations	0		0
Total	17.1		14.4
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Corporate debt securities [Member]
Assets:
Marketable debt securities	287.0		1,001.0
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Government securities [Member]
Assets:
Marketable debt securities	267.2		1,657.8
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Mortgage and other asset backed securities [Member]
Assets:
Marketable debt securities	60.2		512.9
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Marketable equity securities [Member]
Assets:
Investments	0		0
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Venture capital investments [Member]
Assets:
Investments	0		0
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Cash equivalents	0		0
Derivative contracts	0		0
Plan assets for deferred compensation	0		0
Total	27.6		20.3
Liabilities:
Derivative contracts	0		0
Contingent consideration obligations	281.0		293.9
Total	281.0		293.9
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member] | Corporate debt securities [Member]
Assets:
Marketable debt securities	0		0
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member] | Government securities [Member]
Assets:
Marketable debt securities	0		0
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member] | Mortgage and other asset backed securities [Member]
Assets:
Marketable debt securities	0		0
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member] | Marketable equity securities [Member]
Assets:
Investments	0		0
Significant Unobservable Inputs (Level 3) [Member] | Fair Value, Measurements, Recurring [Member] | Venture capital investments [Member]
Assets:
Investments	$ 27.6		$ 20.3