Leases - Narrative (Details) ft² in Thousands, $ in Millions	1 Months Ended	3 Months Ended	9 Months Ended
	Sep. 30, 2021 ft² numberOfExtensionPeriod	Sep. 30, 2023 USD ($) ft² numberOfBuilding numberOfExtensionPeriod campus	Sep. 30, 2023 USD ($) ft² numberOfBuilding numberOfExtensionPeriod campus	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)
Lessee, Lease, Description [Line Items]
Number of campuses | campus		2	2
Decrease in operating lease liabilities			$ (605)	$ 27
Present value of lease liabilities		$ 730	730
Right-of-use assets, operating leases		765	765		$ 121
Embedded Leases
Lessee, Lease, Description [Line Items]
Decrease in the right of use of the asset		262
Decrease in operating lease liabilities		262
Depreciation		161
Present value of lease liabilities		149	149		440
Right-of-use assets, operating leases		$ 161	$ 161		$ 639
MTC South, MTC North and MTC East
Lessee, Lease, Description [Line Items]
Area of office space (in sqft) | ft²		686	686
Number of extension | numberOfExtensionPeriod		3	3
Extension term		5 years	5 years
Finance lease, number of properties | numberOfBuilding		3	3
Cambridge leases
Lessee, Lease, Description [Line Items]
Area of office space (in sqft) | ft²	462	292	292
Number of years	2 years
Lease term	15 years
Number of extension | numberOfExtensionPeriod	2
Extension term	7 years