Cover Page - shares	9 Months Ended
	Sep. 30, 2021	Nov. 10, 2021
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2021
Document Transition Report	false
Entity File Number	001-39484
Entity Registrant Name	METROMILE, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	84-4916134
Entity Address, Address Line One	425 Market Street #700
Entity Address, City or Town	San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94105
City Area Code	888
Local Phone Number	242-5204
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		127,741,367
Current Fiscal Year End Date	--12-31
Amendment Flag	false
Entity Central Index Key	0001819035
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Common Stock
Document Information [Line Items]
Title of 12(b) Security	Common Stock
Trading Symbol	MILE
Security Exchange Name	NASDAQ
Warrant
Document Information [Line Items]
Title of 12(b) Security	Warrants
Trading Symbol	MILEW
Security Exchange Name	NASDAQ