| Document and Entity Information | Apr. 21, 2020 |
| Document And Entity Information [Line Items] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001578845 |
| Document Type | 8-K |
| Document Period End Date | Apr. 21, 2020 |
| Entity Registrant Name | ALLERGAN PLC |
| Entity Incorporation State Country Code | L2 |
| Entity File Number | 001-36867 |
| Entity Tax Identification Number | 98-1114402 |
| Entity Address, Address Line One | Clonshaugh Business and Technology Park |
| Entity Address, Address Line Two | Coolock |
| Entity Address, City or Town | Dublin |
| Entity Address, Postal Zip Code | D17 E400 |
| Entity Address, Country | IE |
| City Area Code | (862) |
| Local Phone Number | 261-7000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Fair Value Measured at Net Asset Value Per Share [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Ordinary Share, par value $0.0001 per share |
| Trading Symbol | AGN |
| Security Exchange Name | NYSE |
| Floating Rate Notes Due 2020 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Floating rate notes due 2020 |
| Trading Symbol | AGN20A |
| Security Exchange Name | NYSE |
| M 0.500 Notes Due 20215 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 0.500% notes due 2021 |
| Trading Symbol | AGN21 |
| Security Exchange Name | NYSE |
| M 1.500 Notes Due 20231 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 1.500% notes due 2023 |
| Trading Symbol | AGN23A |
| Security Exchange Name | NYSE |
| M 1.250 Notes Due 20242 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 1.250% notes due 2024 |
| Trading Symbol | AGN24A |
| Security Exchange Name | NYSE |
| M 2.625 Notes Due 20283 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 2.625% notes due 2028 |
| Trading Symbol | AGN28 |
| Security Exchange Name | NYSE |
| M 2.125 Notes Due 20294 [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 2.125% notes due 2029 |
| Trading Symbol | AGN29 |
| Security Exchange Name | NYSE |
