Description of Operations (Narrative) (Details) $ / shares in Units, $ in Billions	6 Months Ended
	Jun. 30, 2018	May 08, 2018 $ / shares	Apr. 16, 2018 USD ($)
Takeda
Business Acquisition [Line Items]
Potential offer share price (in usd per share) | $ / shares		$ 30.33
New Takeda Shares | Takeda
Business Acquisition [Line Items]
Takeda shares per Shire shares		0.839
Takeda ADS to Takeda share ratio	0.5
Takeda ADS | Takeda
Business Acquisition [Line Items]
Takeda shares per Shire shares		1.678
Disposal Group | Oncology
Business Acquisition [Line Items]
Agreement consideration | $			$ 2.4