Guarantor Financial Information (Condensed Consolidating Statement of Cash Flows) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
CASH FLOWS FROM OPERATING ACTIVITIES:
Net cash provided by/(used in) operating activities	$ 4,256.7	$ 2,658.9	$ 2,337.0
CASH FLOWS FROM INVESTING ACTIVITIES:
Transactions with subsidiaries	0.0	0.0	0.0
Purchases of businesses, net of cash acquired	0.0	(17,476.2)	(5,553.4)
Purchases of PP&E	(798.8)	(648.7)	(114.7)
Proceeds/(payment) from sale of investments	88.6	0.9	85.7
Movements in restricted cash	(13.7)	62.8	(32.0)
Other, net	23.0	(31.0)	(5.5)
Net cash used in investing activities	(700.9)	(18,092.2)	(5,619.9)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from revolving line of credit, long term and short term borrowings	4,236.7	32,443.4	3,760.8
Repayment of revolving line of credit, long term and short term borrowings	(7,681.4)	(16,404.3)	(3,110.9)
Proceeds from intercompany borrowings	0.0	0.0	0.0
Payment of dividend	(281.3)	(171.3)	(134.4)
Debt issuance costs	0.0	(172.3)	(24.1)
Proceeds from issuance of stock for share-based compensation arrangements	134.1	169.2	16.6
Other, net	(27.4)	(38.9)	(69.0)
Net cash (used in)/provided by financing activities	(3,619.3)	15,825.8	439.0
Effect of foreign exchange rate changes on cash and cash equivalents	7.1	0.8	(3.0)
Net (decrease)/increase in cash and cash equivalents	(56.4)	393.3	(2,846.9)
Cash and cash equivalents at beginning of period	528.8	135.5	2,982.4
Cash and cash equivalents at end of period	472.4	528.8	135.5
Eliminations
CASH FLOWS FROM OPERATING ACTIVITIES:
Net cash provided by/(used in) operating activities	0.0	0.0	0.0
CASH FLOWS FROM INVESTING ACTIVITIES:
Transactions with subsidiaries	40,051.9	26,306.8	6,618.2
Purchases of businesses, net of cash acquired		0.0	0.0
Purchases of PP&E	0.0	0.0	0.0
Proceeds/(payment) from sale of investments	0.0	0.0	0.0
Movements in restricted cash	0.0	0.0	0.0
Other, net	0.0	0.0	0.0
Net cash used in investing activities	40,051.9	26,306.8	6,618.2
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from revolving line of credit, long term and short term borrowings	0.0	0.0	0.0
Repayment of revolving line of credit, long term and short term borrowings	0.0	0.0	0.0
Proceeds from intercompany borrowings	(40,051.9)	(26,306.8)	(6,618.2)
Payment of dividend	0.0	0.0	0.0
Debt issuance costs		0.0	0.0
Proceeds from issuance of stock for share-based compensation arrangements	0.0	0.0	0.0
Other, net	0.0	0.0	0.0
Net cash (used in)/provided by financing activities	(40,051.9)	(26,306.8)	(6,618.2)
Effect of foreign exchange rate changes on cash and cash equivalents	0.0	0.0	0.0
Net (decrease)/increase in cash and cash equivalents	0.0	0.0	0.0
Cash and cash equivalents at beginning of period	0.0	0.0	0.0
Cash and cash equivalents at end of period	0.0	0.0	0.0
Shire plc (Parent Guarantor)
CASH FLOWS FROM OPERATING ACTIVITIES:
Net cash provided by/(used in) operating activities	0.0	(136.9)	(133.5)
CASH FLOWS FROM INVESTING ACTIVITIES:
Transactions with subsidiaries	(10,349.3)	(2,890.0)	(3,570.0)
Purchases of businesses, net of cash acquired		0.0	0.0
Purchases of PP&E	0.0	0.0	0.0
Proceeds/(payment) from sale of investments	0.0	0.0	0.0
Movements in restricted cash	0.0	0.0	0.0
Other, net	0.0	0.0	0.0
Net cash used in investing activities	(10,349.3)	(2,890.0)	(3,570.0)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from revolving line of credit, long term and short term borrowings	2,110.0	2,355.0	3,760.0
Repayment of revolving line of credit, long term and short term borrowings	(2,560.0)	(3,405.0)	(3,110.0)
Proceeds from intercompany borrowings	10,801.5	4,077.8	3,048.2
Payment of dividend	(35.8)	(20.7)	(6.8)
Debt issuance costs		0.0	(4.5)
Proceeds from issuance of stock for share-based compensation arrangements	33.6	19.8	16.6
Other, net	0.0	0.0	0.0
Net cash (used in)/provided by financing activities	10,349.3	3,026.9	3,703.5
Effect of foreign exchange rate changes on cash and cash equivalents	0.0	0.0	0.0
Net (decrease)/increase in cash and cash equivalents	0.0	0.0	0.0
Cash and cash equivalents at beginning of period	0.0	0.0	0.0
Cash and cash equivalents at end of period	0.0	0.0	0.0
SAIIDAC (SAIIDAC Notes Subsidiary Issuer)
CASH FLOWS FROM OPERATING ACTIVITIES:
Net cash provided by/(used in) operating activities	6.6	232.8	0.0
CASH FLOWS FROM INVESTING ACTIVITIES:
Transactions with subsidiaries	(2,670.2)	(18,228.8)	0.0
Purchases of businesses, net of cash acquired		0.0	0.0
Purchases of PP&E	0.0	0.0	0.0
Proceeds/(payment) from sale of investments	0.0	0.0	0.0
Movements in restricted cash	0.0	0.0	0.0
Other, net	0.0	0.0	0.0
Net cash used in investing activities	(2,670.2)	(18,228.8)	0.0
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from revolving line of credit, long term and short term borrowings	1,610.0	30,079.9	0.0
Repayment of revolving line of credit, long term and short term borrowings	(4,600.0)	(13,009.2)	0.0
Proceeds from intercompany borrowings	5,653.6	1,097.6	0.0
Payment of dividend	0.0	0.0	0.0
Debt issuance costs		(172.3)	0.0
Proceeds from issuance of stock for share-based compensation arrangements	0.0	0.0	0.0
Other, net	0.0	0.0	0.0
Net cash (used in)/provided by financing activities	2,663.6	17,996.0	0.0
Effect of foreign exchange rate changes on cash and cash equivalents	0.0	0.0	0.0
Net (decrease)/increase in cash and cash equivalents	0.0	0.0	0.0
Cash and cash equivalents at beginning of period	0.0	0.0	0.0
Cash and cash equivalents at end of period	0.0	0.0	0.0
Baxalta Inc. (Baxalta Notes Subsidiary Issuer and SAIIDAC Notes Subsidiary Guarantor)
CASH FLOWS FROM OPERATING ACTIVITIES:
Net cash provided by/(used in) operating activities	(13.1)	(51.0)	0.0
CASH FLOWS FROM INVESTING ACTIVITIES:
Transactions with subsidiaries	(5,604.9)	(480.7)	0.0
Purchases of businesses, net of cash acquired		0.0	0.0
Purchases of PP&E	0.0	(11.1)	0.0
Proceeds/(payment) from sale of investments	(9.7)	0.0	0.0
Movements in restricted cash	0.0	0.0	0.0
Other, net	0.0	0.0	0.0
Net cash used in investing activities	(5,614.6)	(491.8)	0.0
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from revolving line of credit, long term and short term borrowings	0.0	0.0	0.0
Repayment of revolving line of credit, long term and short term borrowings	0.0	0.0	0.0
Proceeds from intercompany borrowings	5,582.6	521.9	0.0
Payment of dividend	0.0	0.0	0.0
Debt issuance costs		0.0	0.0
Proceeds from issuance of stock for share-based compensation arrangements	4.8	132.9	0.0
Other, net	(0.9)	(70.3)	0.0
Net cash (used in)/provided by financing activities	5,586.5	584.5	0.0
Effect of foreign exchange rate changes on cash and cash equivalents	0.0	0.0	0.0
Net (decrease)/increase in cash and cash equivalents	(41.2)	41.7	0.0
Cash and cash equivalents at beginning of period	41.7	0.0	0.0
Cash and cash equivalents at end of period	0.5	41.7	0.0
Non-Guarantor Non-Issuer Subsidiaries
CASH FLOWS FROM OPERATING ACTIVITIES:
Net cash provided by/(used in) operating activities	4,263.2	2,614.0	2,470.5
CASH FLOWS FROM INVESTING ACTIVITIES:
Transactions with subsidiaries	(21,427.5)	(4,707.3)	(3,048.2)
Purchases of businesses, net of cash acquired		(17,476.2)	(5,553.4)
Purchases of PP&E	(798.8)	(637.6)	(114.7)
Proceeds/(payment) from sale of investments	98.3	0.9	85.7
Movements in restricted cash	(13.7)	62.8	(32.0)
Other, net	23.0	(31.0)	(5.5)
Net cash used in investing activities	(22,118.7)	(22,788.4)	(8,668.1)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from revolving line of credit, long term and short term borrowings	516.7	8.5	0.8
Repayment of revolving line of credit, long term and short term borrowings	(521.4)	9.9	(0.9)
Proceeds from intercompany borrowings	18,014.2	20,609.5	3,570.0
Payment of dividend	(245.5)	(150.6)	(127.6)
Debt issuance costs		0.0	(19.6)
Proceeds from issuance of stock for share-based compensation arrangements	95.7	16.5	0.0
Other, net	(26.5)	31.4	(69.0)
Net cash (used in)/provided by financing activities	17,833.2	20,525.2	3,353.7
Effect of foreign exchange rate changes on cash and cash equivalents	7.1	0.8	(3.0)
Net (decrease)/increase in cash and cash equivalents	(15.2)	351.6	(2,846.9)
Cash and cash equivalents at beginning of period	487.1	135.5	2,982.4
Cash and cash equivalents at end of period	471.9	487.1	135.5
Non-Guarantor Subsidiaries of Baxalta Notes
CASH FLOWS FROM OPERATING ACTIVITIES:
Net cash provided by/(used in) operating activities	4,269.8	2,846.8	2,470.5
CASH FLOWS FROM INVESTING ACTIVITIES:
Transactions with subsidiaries	(24,097.7)	(22,936.1)	(3,048.2)
Purchases of businesses, net of cash acquired		(17,476.2)	(5,553.4)
Purchases of PP&E	(798.8)	(637.6)	(114.7)
Proceeds/(payment) from sale of investments	98.3	0.9	85.7
Movements in restricted cash	(13.7)	62.8	(32.0)
Other, net	23.0	(31.0)	(5.5)
Net cash used in investing activities	(24,788.9)	(41,017.2)	(8,668.1)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from revolving line of credit, long term and short term borrowings	2,126.7	30,088.4	0.8
Repayment of revolving line of credit, long term and short term borrowings	(5,121.4)	(12,999.3)	(0.9)
Proceeds from intercompany borrowings	23,667.8	21,707.1	3,570.0
Payment of dividend	(245.5)	(150.6)	(127.6)
Debt issuance costs		(172.3)	(19.6)
Proceeds from issuance of stock for share-based compensation arrangements	95.7	16.5	0.0
Other, net	(26.5)	31.4	(69.0)
Net cash (used in)/provided by financing activities	20,496.8	38,521.2	3,353.7
Effect of foreign exchange rate changes on cash and cash equivalents	7.1	0.8	(3.0)
Net (decrease)/increase in cash and cash equivalents	(15.2)	351.6	(2,846.9)
Cash and cash equivalents at beginning of period	487.1	135.5	2,982.4
Cash and cash equivalents at end of period	$ 471.9	$ 487.1	$ 135.5