Consolidated Statement of Changes in Equity - USD ($) shares in Millions	Total	Common stock	Additional paid-in capital	Treasury stock	Accumulated other comprehensive (loss)/income	Retained earnings	New Shire Income Access Share Trust	New Shire Income Access Share Trust Capital account	New Shire Income Access Share Trust Revenue account
Beginning balance at Dec. 31, 2014	$ 8,662,900,000	$ 58,700,000	$ 4,338,000,000	$ (345,900,000)	$ (31,500,000)	$ 4,643,600,000	$ 0	$ 0	$ 0
Beginning balance (in shares) at Dec. 31, 2014		599.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,303,400,000					1,303,400,000	127,700,000	0	127,700,000
Other comprehensive income (loss), net of tax	(152,300,000)				(152,300,000)
Options exercised (in shares)		2.0
Options exercised	16,600,000	$ 200,000	16,400,000
Share-based compensation	100,300,000		100,300,000
Tax benefit associated with exercise of stock options	31,600,000		31,600,000
Shares released by employee benefit trust to satisfy exercise of stock options	1,000,000			25,300,000		(24,300,000)
Dividends	(134,400,000)					(134,400,000)	(127,700,000)	0	(127,700,000)
Ending balance at Dec. 31, 2015	9,829,100,000	$ 58,900,000	4,486,300,000	(320,600,000)	(183,800,000)	5,788,300,000	0	0	0
Ending balance (in shares) at Dec. 31, 2015		601.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	327,400,000					327,400,000	150,600,000	0	150,600,000
Other comprehensive income (loss), net of tax	(1,313,800,000)				(1,313,800,000)
Shares issued under employee benefit plans and other (in shares)		5.9
Shares issued under employee benefit plans and other	138,800,000	$ 400,000	138,400,000
Shares issued for the acquisition of Baxalta (in shares)		305.2
Shares issued for the acquisition of Baxalta	19,810,900,000	$ 22,000,000	19,788,900,000
Share-based compensation	318,500,000		318,500,000
Tax benefit associated with exercise of stock options	8,800,000		8,800,000
Shares released by employee benefit trust to satisfy exercise of stock options	(400,000)			18,700,000		(19,100,000)
Dividends	(171,300,000.0)					(171,300,000)	(150,600,000)	0	(150,600,000)
Ending balance at Dec. 31, 2016	$ 28,948,000,000	$ 81,300,000	24,740,900,000	(301,900,000)	(1,497,600,000)	5,925,300,000	0	0	0
Ending balance (in shares) at Dec. 31, 2016	912.2	912.2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative-effect adjustment from adoption of ASU 2016-09	$ 34,700,000		10,700,000			24,000,000
Net income	4,271,500,000					4,271,500,000	245,600,000	0	245,600,000
Other comprehensive income (loss), net of tax	2,872,600,000				2,872,600,000
Shares issued under employee benefit plans and other (in shares)		4.9
Shares issued under employee benefit plans and other	156,000,000	$ 300,000	155,700,000
Share-based compensation	174,900,000		174,900,000
Tax benefit associated with exercise of stock options	0
Shares released by employee benefit trust to satisfy exercise of stock options	0			18,900,000		(18,900,000)
Dividends	(281,300,000)					(281,300,000)	(245,600,000)	0	(245,600,000)
Ending balance at Dec. 31, 2017	$ 36,176,400,000	$ 81,600,000	$ 25,082,200,000	$ (283,000,000)	$ 1,375,000,000	$ 9,920,600,000	$ 0	$ 0	$ 0
Ending balance (in shares) at Dec. 31, 2017	917.1	917.1