Collaborative And Other Arrangements Narrative (Details) € / shares in Units, € in Millions, shares in Millions, $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Aug. 31, 2019 USD ($)	Sep. 30, 2019 USD ($) shares	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) shares	Sep. 30, 2018 USD ($)	Oct. 31, 2019 EUR (€) € / shares shares	Aug. 23, 2019 USD ($) shares	Aug. 23, 2019 € / shares	Jan. 19, 2016 USD ($) shares	Jan. 19, 2016 € / shares
Collaborative and Other Arrangements [Line Items]
Research and development expenses		$ 4,990	$ 939	$ 7,207	$ 3,068
Galapagos [Member]
Collaborative and Other Arrangements [Line Items]
Investment owned, balance, shares | shares		13.6		13.6			6.8		6.8
Share price | € / shares								€ 140.59		€ 58
Contractual lock-up period	5 years
Equity securities, FV-NI, cost							$ 1,130		$ 357
Payment for license, option rights and equity investments upon closing	$ 5,050
Equity method investment, ownership percentage							22.00%
Issuance discount							$ 63
Research and development expenses		$ 3,920
Potential milestone payment upon marketing approval GLPG-1690							325
Potential option exercise fee for GLPG-1972							250
Potential milestone payments for GLPG-1972 after option exercise							750
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%
Maximum ownership percentage in Galapagos based on the terms of the subscription agreement							29.90%
Standstill restricting term	10 years
Minimum ownership percentage in Galapagos based on the terms of the subscription agreement							20.10%
Potential future development and regulatory milestone									755
Potential future sales-based milestone									$ 600
Potential future tiered royalty payment low-end									20.00%
Potential future tiered royalty payment high-end									30.00%
Galapagos [Member] | Subsequent Event [Member]
Collaborative and Other Arrangements [Line Items]
Investment owned, balance, shares | shares						16.2
Share price | € / shares						€ 140.59
Equity securities, FV-NI, cost | €						€ 368
Equity method investment, ownership percentage						25.10%
Warrant exercised, shares | shares						2.6
Other Collaboration Arrangements [Member]
Collaborative and Other Arrangements [Line Items]
Cash outflows related to collaborative and other similar arrangements		54	29	$ 447	333
Up-front collaboration and licensing expenses related to collaborative and other similar arrangements		$ 40	$ 0	$ 331	$ 160