Revenue Recognition
Revenue is recognized when control of the promised goods or services is transferred to our customers, in an amount that reflects the consideration we expect to be entitled to in exchange for those goods and services.
We disaggregate revenue into four categories as presented on our statements of income:
Lease Revenue
Lease revenue, which includes operating lease revenue and finance lease revenue, is our primary source of revenue.
Operating Lease Revenue
We lease railcars, locomotives, aircraft spare engines, and tank containers under full-service and net operating leases. We price full-service leases as an integrated service that includes amounts related to maintenance, insurance, and ad valorem taxes. We do not offer stand-alone maintenance service contracts. Operating lease revenue is within the scope of Topic 842, and we have elected not to separate non-lease components from the associated lease component for qualifying leases. Operating lease revenue is recognized on a straight-line basis over the term of the underlying lease. As a result, lease revenue may not be recognized in the same period as maintenance and other costs, which we expense as incurred. Variable rents are recognized when applicable contingencies are resolved. Revenue is not recognized if collectability is not probable. See "Note 5. Leases."
Finance Lease Revenue
In certain cases, we lease railcars and tank containers that, at lease inception or upon modification, are classified as finance leases. In accordance with Topic 842, finance lease revenue is recognized using the effective interest method, using the interest rate implicit in the lease. See "Note 5. Leases."
Non-Dedicated Engine Revenue
Certain of our owned aircraft spare engines are part of a pool of non-dedicated spare engines managed under a capacity agreement with Rolls-Royce plc and its affiliates (collectively "Rolls-Royce"). Revenue is earned based on our ability to meet engine capacity requirements under the agreement, which requires us to enroll a minimum number of engines in a pool of non-dedicated spare engines for short-term lease to Rolls-Royce customers. We recognize revenue based on our right to receive a portion of the revenue earned by the pool, which is calculated based on the average engine flight hours reported for each type of engine enrolled into the pool.
Marine Operating Revenue
Historically, we generated marine operating revenue through shipping services completed by our marine vessels. All marine vessels were sold as of December 31, 2023.
Other Revenue
Other revenue is comprised of customer repair revenue, termination fees, interest income, and other miscellaneous revenues. Select components of other revenue are within the scope of ASC Topic 606, Revenue from Contracts with Customers. Revenue attributable to variable lease components is recognized when earned, in accordance with Topic 842.