Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2017	Oct. 19, 2017
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q3
Trading Symbol	GOOG, GOOGL
Entity Registrant Name	Alphabet Inc.
Entity Central Index Key	0001652044
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Class A Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		298,279,094
Class B Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		47,043,867
Class C Capital Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		349,479,150