Earnings Per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011
Schedule of Calculation of Numerator and Denominator in Earnings Per Share
Net income attributable to Shire plc	$ 238.4		$ 211.3
Interest on convertible bonds, net of tax	8.4		8.4
Numerator for diluted earnings per share	$ 246.8		$ 219.7
Schedule of Weighted Average Number of Shares
Basic	553.5	[1]	549.5	[1]
Effect of dilutive shares:
Share based awards to employees	8.6	[2]	10.9	[2]
Convertible bonds 2.75% due 2014	33.5	[3]	33.2	[3]
Diluted	595.6		593.6
Earning per ordinary share - basic
Earnings per ordinary share attributable to Shire plc shareholders - basic	$ 0.431		$ 0.385
Earnings per ordinary share - diluted
Earnings per ordinary share attributable to Shire plc shareholders - diluted	$ 0.414		$ 0.370
Share Awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	6.1	[4]	7.5	[4]

[1] Excludes shares purchased by the EBT and presented by the Company as treasury stock.

[2] Calculated using the treasury stock method.

[3] Calculated using the ‘if-converted’ method.

[4] Certain stock options have been excluded from the calculation of diluted EPS because (a) their exercise prices exceeded Shire plc’s average share price during the calculation period or (b) the required performance conditions were not satisfied as at the balance sheet date.