Leases - Narrative (Details) ft² in Thousands, $ in Millions	Mar. 31, 2023 USD ($) ft² numberOfExtensionPeriod campus	Dec. 31, 2022 USD ($)
Lessee, Lease, Description [Line Items]
Number of campuses | campus	2
Present value of lease liabilities	$ 124
Right-of-use assets, operating leases	117	$ 121
Embedded Leases
Lessee, Lease, Description [Line Items]
Present value of lease liabilities	410	440
Right-of-use assets, operating leases	$ 587	$ 639
MTC South, MTC North and MTC East
Lessee, Lease, Description [Line Items]
Area of office space (in sqft) | ft²	686
Number of extension | numberOfExtensionPeriod	3
Extension term	5 years
Cambridge leases
Lessee, Lease, Description [Line Items]
Area of office space (in sqft) | ft²	292