Earnings Per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Schedule of Calculation of Numerator and Denominator in Earnings Per Share
Numerator for basic earnings per share	$ 42.0	$ 227.2	$ 237.8	$ 238.4	$ 255.3	$ 192.9	$ 205.5	$ 211.3	$ 745.4		$ 865.0		$ 588.0
Interest on convertible bonds, net of tax									31.3		33.6		33.5
Numerator for diluted earnings per share									$ 776.7		$ 898.6		$ 621.5
Schedule of Weighted Average Number of Shares
Basic									555.4	[1]	551.1	[1]	546.2	[1]
Effect of dilutive shares:
Share based awards to employees									4.6	[2]	10.9	[2]	10.9	[2]
Convertible bonds 2.75% due 2014									33.5	[3]	33.4	[3]	33.2	[3]
Diluted									593.5		595.4		590.3
Earning per ordinary share - basic
Earnings per ordinary share attributable to Shire plc shareholders - basic	$ 0.075	$ 0.409	$ 0.427	$ 0.431	$ 0.464	$ 0.350	$ 0.372	$ 0.385	$ 1.342		$ 1.569		$ 1.077
Earnings per ordinary share - diluted
Earnings per ordinary share attributable to Shire plc shareholders - diluted	$ 0.074	$ 0.396	$ 0.413	$ 0.414	$ 0.444	$ 0.339	$ 0.359	$ 0.370	$ 1.309		$ 1.509		$ 1.053
Share Awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share									6.7	[4]	2.9	[4]	5.4	[4]

[1] Excludes shares purchased by the EBT and under the share buy-back program and presented by Shire 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.