License Funding and Other Agreements Related to the CVR - Additional Information (Details) $ in Millions	1 Months Ended	9 Months Ended
	May 31, 2019 USD ($)	Sep. 30, 2020 USD ($) Right	Mar. 23, 2017 USD ($)
National Institute of Health
Research And Development Arrangement Contract To Perform For Others [Line Items]
Grant term	5 years
Grants receivable	$ 1.5
Qualifying expenses		$ 0.7
National Institute of Health | Funding Agreement
Research And Development Arrangement Contract To Perform For Others [Line Items]
Qualifying expenses		$ 0.7
Novartis License Agreement | Novartis International Pharmaceutical Ltd.
Research And Development Arrangement Contract To Perform For Others [Line Items]
License agreement termination description		The agreement may be terminated by either party upon a material breach of obligation by the other party that is not cured with 60 days after written notice. resTORbio may terminate the agreement in its entirety or on a product-by-product or country-by-country basis with or without cause with 60 days’ prior written notice.
Novartis License Agreement | Novartis International Pharmaceutical Ltd. | Maximum
Research And Development Arrangement Contract To Perform For Others [Line Items]
Aggregate amount payable upon satisfaction of clinical milestones			$ 4.3
Aggregate amount payable upon satisfaction of regulatory milestones for first indication approved			24.0
Aggregate amount payable upon satisfaction of regulatory milestones for second indication approved			18.0
Aggregate amount payable upon satisfaction of commercial milestones			$ 125.0
Contingent Value Rights Agreement [Member] | COVID-19 [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Common stock value right | Right		1
Total fees and expenses related to clinical trials		$ 3.0