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Collaborative and Other Arrangements - Collaborative Arrangements Narrative (Details) € / shares in Units, € in Millions, shares in Millions, $ in Millions	1 Months Ended		3 Months Ended		12 Months Ended
	Aug. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 09, 2019 USD ($) shares	Nov. 06, 2019 € / shares shares	Aug. 23, 2019 USD ($) shares	Aug. 23, 2019 € / shares	Jul. 19, 2018 USD ($)	Jul. 19, 2018 EUR (€)	Jan. 19, 2016 USD ($) shares	Jan. 19, 2016 € / shares
Collaborative Arrangements
Prepaid and other current assets		$ 1,606			$ 1,440	$ 1,606
Research and development expenses					9,106	5,018	$ 3,734
Goodwill		4,117			4,117	4,117
Cost of goods sold					$ 4,675	4,853	4,371
Upfront collaboration and licensing expense [Member]
Collaborative Arrangements
Research and development expenses			$ 3,920
Gadeta [Member]
Collaborative Arrangements
Collaborative Arrangement-Potential Option Payout Upon Exercise \| €													€ 300
Indefinite-lived Intangible Assets Acquired				$ 117
Noncontrolling Interest in Variable Interest Entity												$ 82
Goodwill												$ 0
Janssen Pharmaceuticals [Member]
Collaborative Arrangements
Purchase price of goods less specified amount, maximum percentage					30.00%
Cost of goods sold					$ 574	608	561
Japan Tobacco [Member]
Collaborative Arrangements
Finite-lived Intangible Assets Acquired						550
Prepaid and other current assets		9				$ 9
Finite-Lived Intangible Asset, Useful Life						9 years
Royalty Expense					358	$ 452	400
Initial Consideration for Acquisition of Rights to Market and Distribute Certain Products in Japan		559
Payments to Acquire Management Contract Rights		$ 194			365
Galapagos [Member]
Collaborative Arrangements
Standstill Restricting Term	10 years
Available-for-sale Securities, Equity Securities, Noncurrent								$ 586		$ 1,130				$ 357
Share Price \| € / shares											€ 140.59				€ 58
Investment Owned, Balance, Shares \| shares								16.7	2.6	6.8				6.8
Class of Warrant or Right, Exercise Price of Warrants or Rights \| € / shares									€ 140.59
Equity Method Investment, Ownership Percentage								25.80%
Maximum Ownership Percentage in Galapagos Based on the Terms of the Subscription Agreement										29.90%
Minimum Ownership Percentage in Galapagos Based on the Terms of the Subscription Agreement										20.10%
Potential Milestone for GLPG-1972 after Option Exercise					640					$ 750
Potential Future Sales-based Milestone					$ 600
Potential Future Tiered Royalty Payment Low-end					20.00%
Potential Future Tiered Royalty Payment High-end					30.00%
Payment for License, Option Rights and Equity Investments Upon Closing	$ 5,050
Issuance discount										63
Potential Milestone Payment Upon Marketing Approval GLPG-1690										325
Potential Option Exercise Fee for GLPG-1972										250
Potential Option Exercise Fee Per Program										$ 150
Potential Sales Based Tiered Royalty Low-end										20.00%
Potential Sales Based Tiered Royalties High-end										24.00%
Bristol-Myers-Squibb [Member]
Collaborative Arrangements
Cost of goods sold					$ 58	198
Other Collaboration Arrangements [Member]
Collaborative Arrangements
Up-front Collaboration and Licensing Expenses Related to Other Collaboration Arrangements That Are Not Individually Significant					331	278
Cash Outflows Related to Other Collaboration Arrangements That Are Not Individually Significant					$ 467	$ 474	$ 0