| Document and Entity Information | Dec. 16, 2020 |
| Document And Entity Information [Line Items] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001652044 |
| Document Type | 8-K |
| Document Period End Date | Dec. 16, 2020 |
| Entity Registrant Name | ALPHABET INC. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-37580 |
| Entity Tax Identification Number | 61-1767919 |
| Entity Address, Address Line One | 1600 Amphitheatre Parkway |
| Entity Address, City or Town | Mountain View |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 94043 |
| City Area Code | (650) |
| Local Phone Number | 253-0000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Common Class B [Member] | |
| Document And Entity Information [Line Items] | |
| Security Exchange Name | NASDAQ |
| Security 12b Title | Class A Common Stock, $0.001 par value |
| Trading Symbol | GOOGL |
| Capital Class C [Member] | |
| Document And Entity Information [Line Items] | |
| Security Exchange Name | NASDAQ |
| Security 12b Title | Class C Capital Stock, $0.001 par value |
| Trading Symbol | GOOG |
