ACQUISITIONS - Narrative (Details) $ / shares in Units, $ in Millions					3 Months Ended			12 Months Ended
	Oct. 19, 2015 USD ($)	Oct. 01, 2015 USD ($)	Apr. 01, 2015 USD ($) product $ / shares	Feb. 23, 2015 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)	Feb. 10, 2015 USD ($)
Business Acquisition [Line Items]
Acquisition-related contingent consideration					$ 146.3	$ 196.8		$ 196.8
Acquisition of businesses, contingent and deferred consideration obligations at fair value					0.0		$ 286.9
Purchase price net of cash received					18.5		$ 795.0
Pro forma acquisition accounting adjustment on inventory sold subsequent to acquisition date								24.0
1.5% Convertible Notes Due March 2019 | Convertible Debt
Business Acquisition [Line Items]
Stated interest rate on debt (as a percent)			1.50%
Estimated fair value of warrant transactions						1,080.0		1,080.0
2.75% Convertible Notes Due May 2015 | Convertible Debt
Business Acquisition [Line Items]
Stated interest rate on debt (as a percent)			2.75%
Amoun
Business Acquisition [Line Items]
Total fair value of consideration transferred	$ 911.0
Acquisition of noncontrolling interest	847.0
Acquisition-related contingent consideration	75.0
Acquisition of businesses, contingent and deferred consideration obligations at fair value	$ 64.0
Accounts receivable, net					64.2
Accounts receivable, gross					66.0
Expected uncollectible of trade accounts receivable acquired					2.0
Deferred tax liabilities					130.0
Aggregate purchase price					911.2
Current liabilities					30.8
Sprout Pharmaceuticals, Inc.
Business Acquisition [Line Items]
Total fair value of consideration transferred		$ 530.0			500.0
Acquisition-related contingent consideration		422.0
Acquisition of businesses, contingent and deferred consideration obligations at fair value					495.0
Total fair value of consideration transferred		1,450.0
Purchase obligation		200.0
Commencement trigger, sales revenue		1,000.0
Aggregate purchase price		1,446.5
Current liabilities		4.4
Salix
Business Acquisition [Line Items]
Total fair value of consideration transferred			$ 13,132.0
Weighted- average useful lives (Years)	9 years		11 years
Number of products in product portfolio (more than) | product			20
Par value per share of common stock (in dollars per share) | $ / shares			$ 0.001
Per share consideration (in usd per share) | $ / shares			$ 173.00
Cash consideration paid for Salix’s restricted stock that was accelerated at the closing of the Salix Acquisition			$ (164.5)
Inventory adjustments			108.0
Estimated fair value of derivatives			1,270.0
Estimated insurance recoveries			$ 80.0
Accrual for potential losses and legal costs						336.0		336.0
Accrual for returns and rebates						375.0		375.0
Range of potential milestone payment, high						650.0		650.0
Contingent consideration, short term portion						(334.1)		(334.1)
Deferred tax assets						303.0		303.0
Deferred tax liabilities						3,730.0		3,730.0
Aggregate purchase price						13,132.0		13,132.0
Current liabilities						1,939.2		1,939.2
Salix | Xifaxan
Business Acquisition [Line Items]
IPR&D asset fair value						$ 4,790.0		$ 4,790.0
Salix | 1.5% Convertible Notes Due March 2019 | Convertible Debt
Business Acquisition [Line Items]
Stated interest rate on debt (as a percent)			1.50%			1.50%		1.50%
Salix | 2.75% Convertible Notes Due May 2015 | Convertible Debt
Business Acquisition [Line Items]
Stated interest rate on debt (as a percent)			2.75%
Other 2015 Acquisitions
Business Acquisition [Line Items]
Total fair value of consideration transferred								$ 1,410.0
Acquisition of businesses, contingent and deferred consideration obligations at fair value								191.0
Accounts receivable, net					46.5
Accounts receivable, gross					$ 51.0
Weighted- average useful lives (Years)					8 years
Aggregate purchase price					$ 1,412.2
Allowance for doubtful accounts					4.0
Current liabilities					127.8
Non-current liabilities					117.2
Dendreon
Business Acquisition [Line Items]
Acquisition of noncontrolling interest				$ 495.0
Purchase price net of cash received				415.0
Cash received from acquisition				80.0
Stock consideration transferred				$ 50.0
Marathon
Business Acquisition [Line Items]
Acquisition-related contingent consideration					$ 10.0	$ 35.0		35.0
Range of potential milestone payment, high						200.0		200.0
Aggregate purchase price									$ 286.0
Assumed liability owed to a third party									$ 64.0
Current liabilities						41.0		41.0
Non-current liabilities						46.0		46.0
Brodalumab [Member]
Business Acquisition [Line Items]
Upfront payment		$ 100.0
Restricted Stock | Salix
Business Acquisition [Line Items]
Per share consideration (in usd per share) | $ / shares			$ 173.00
Development and Sales Based Milestones | Salix
Business Acquisition [Line Items]
Range of potential milestone payment, high						250.0		250.0
Pre-launch Milestone Payments | Brodalumab [Member]
Business Acquisition [Line Items]
Range of potential milestone payment, high						170.0		170.0
Sales Based Milestone Payments [Member] | Brodalumab [Member]
Business Acquisition [Line Items]
Range of potential milestone payment, high						175.0		$ 175.0
Restricted Stock | Salix
Business Acquisition [Line Items]
Cash consideration paid for Salix’s restricted stock that was accelerated at the closing of the Salix Acquisition			$ (165.0)
Acquired IPR&D | Salix
Business Acquisition [Line Items]
Weighted- average useful lives (Years)								10 years
Acquired IPR&D | Maximum | Salix
Business Acquisition [Line Items]
Fair value discount rate								9.50%
Acquired IPR&D | Minimum | Salix
Business Acquisition [Line Items]
Fair value discount rate								11.00%
Other (Income) Expense | Amoun
Business Acquisition [Line Items]
Payments to employees						$ 12.0
Product brands | Sprout Pharmaceuticals, Inc.
Business Acquisition [Line Items]
Weighted- average useful lives (Years)		11 years
Product brands | Salix
Business Acquisition [Line Items]
Weighted- average useful lives (Years)	9 years		10 years
Product brands | Other 2015 Acquisitions
Business Acquisition [Line Items]
Weighted- average useful lives (Years)					7 years