Earnings Per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Schedule of Calculation of Numerator and Denominator in Earnings Per Share
Income from continuing operations, net of taxes									$ 865.0		$ 588.0		$ 503.8
Loss from discontinued operations									0		0		(12.4)
Add: Net loss attributable to the noncontrolling interest in subsidiaries									0		0		0.2
Net income attributable to Shire plc	255.3	192.9	205.5	211.3	165.3	96.3	160.5	165.9	865.0		588.0		491.6
Interest on convertible bonds, net of tax									33.6	[1]	33.5	[1]	0	[1]
Numerator for diluted earnings per share									$ 898.6		$ 621.5		$ 491.6
Schedule of Weighted Average Number of Shares
Basic									551.1	[2]	546.2	[2]	540.7	[2]
Effect of dilutive shares:
Share based awards to employees									10.9	[3]	10.9	[3]	7.3	[3]
Convertible bonds 2.75% due 2014									33.4	[4]	33.2	[4]	0	[4]
Diluted									595.4		590.3		548.0
Earning per ordinary share - basic
Earnings from continuing operations attributable to Shire plc shareholders									$ 1.569		$ 1.077		$ 0.932
Loss from discontinued operations attributable to Shire plc shareholders									$ 0.000		$ 0.000		$ (0.023)
Earnings per ordinary share attributable to Shire plc shareholders - basic	$ 0.464	$ 0.350	$ 0.372	$ 0.385	$ 0.301	$ 0.176	$ 0.294	$ 0.305	$ 1.569		$ 1.077		$ 0.909
Earnings per ordinary share - diluted
Earnings from continuing operations attributable to Shire plc shareholders									$ 1.509		$ 1.053		$ 0.919
Loss from discontinued operations attributable to Shire plc shareholders									$ 0.000		$ 0.000		$ (0.022)
Earnings per ordinary share attributable to Shire plc shareholders - diluted	$ 0.444	$ 0.339	$ 0.359	$ 0.370	$ 0.294	$ 0.173	$ 0.286	$ 0.297	$ 1.509		$ 1.053		$ 0.897
Share Awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share									2.9	[5]	5.4	[5]	16.4	[5]
Convertible Bonds 2.75% due 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share									0	[6]	0	[6]	33.2	[6]

[1] For the year to December 31, 2009 interest on the convertible bonds has not been added back as the effect would be anti-dilutive.

[2] Excludes shares purchased by the ESOT and presented by the Company as treasury stock.

[3] Calculated using the treasury stock method.

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

[5] 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) satisfaction of the required performance/market conditions cannot be measured until the conclusion of the performance period.

[6] For the year to December 31, 2009 the ordinary shares underlying the convertible bonds have not been included in the calculation of the diluted weighted average number of shares, as the effect of their inclusion would be anti-dilutive.