Delta Air Lines, Inc., a Delaware corporation, provides scheduled air transportation for passengers and cargo throughout the United States ("U.S.") and around the world. Our Consolidated Financial Statements include the accounts of Delta Air Lines, Inc. and our consolidated subsidiaries and have been prepared in accordance with accounting principles generally accepted in the U.S. ("GAAP"). We are the primary beneficiary of, and have a controlling financial interest in, certain immaterial entities in which we have voting rights of 50% or less, which we consolidate in our financial results.

We have marketing alliances with other airlines to enhance our access to domestic and international markets. These arrangements may include codesharing, reciprocal loyalty program benefits, shared or reciprocal access to passenger lounges, joint promotions, common use of airport gates and ticket counters, ticket office co-location and other marketing agreements. We have received antitrust immunity for certain marketing arrangements, which enables us to offer a more integrated route network and develop common sales, marketing and discount programs for customers. Some of our marketing arrangements provide for the sharing of revenues and expenses. Revenues and expenses associated with collaborative arrangements are presented on a gross basis in the applicable line items on our Consolidated Statements of Operations ("income statement").

Until 2021, we allocated certain costs (such as landing fees and other rents, salaries and related costs and contracted services) to regional carrier expense in our income statement based on relevant statistics (such as passenger counts). Beginning in 2021 we ceased performing this allocation and have reclassified the costs presented in prior periods to align with this presentation. This reclassification better reflects the nature of, and how management views, these regional carrier related expenses. This allocation was approximately $900 million in 2020 and $1.4 billion in 2019. The amounts in regional carrier expense under the current presentation represent the accrual of payments to our regional carriers under capacity purchase agreements, maintenance costs related to our regional fleet and the expenses of our wholly owned regional subsidiary, Endeavor Air, Inc.

We are required to make estimates and assumptions when preparing our Consolidated Financial Statements in accordance with GAAP. These estimates and assumptions affect the amounts reported in our Consolidated Financial Statements and the accompanying notes. Actual results could differ materially from those estimates.

Government Assistance. In 2021, the Financial Accounting Standards Board issued Accounting Standards Update ("ASU") No. 2021-10, "Government Assistance (Topic 832): Disclosures by Business Entities about Government Assistance." This ASU will require certain disclosures about the significant terms and conditions of material government assistance agreements in order to provide more consistent information to users of the financial statements. This standard is effective for annual reporting periods beginning after December 15, 2021, and early adoption is permitted. We determined that our material government assistance agreements are the payroll support program agreements under the Coronavirus Aid, Relief and Economic Security Act ("CARES Act") and the program extensions, and we adopted the new standard in 2021. See Note 6, "Debt," where we reflect the requirements of this new standard as it relates to our payroll support program disclosures.

Short-term, highly liquid investments with maturities of three months or less when purchased are classified as cash and cash equivalents. Investments with maturities of greater than three months, but not in excess of one year, when purchased are classified as short-term investments. Investments with maturities beyond one year when purchased may be classified as short-term investments if they are expected to be available to support our short-term liquidity needs. Our short-term investments are classified as fair value investments and gains and losses are recorded in non-operating expense.


Reconciliation of cash, cash equivalents and restricted cash
	December 31,
(in millions)	2021		2020		2019
Current assets:
Cash and cash equivalents	$	7,933	$	8,307	$	2,882
Restricted cash included in prepaid expenses and other	163		192		212
Noncurrent assets:
Cash restricted for airport construction	473		1,556		636
Total cash, cash equivalents and restricted cash	$	8,569	$	10,055	$	3,730

Fuel. As part of our strategy to mitigate the cost of the refining margin reflected in the price of jet fuel, our wholly owned subsidiary, Monroe Energy, LLC ("Monroe"), operates the Trainer oil refinery. Refined products (finished goods) and feedstock and blendstock inventories (work-in-process) are both carried at the lower of cost and net realizable value. We use jet fuel in our airline operations that is produced by the refinery and procured through the exchange with third parties of gasoline, diesel and other refined products ("non-jet fuel products") the refinery produces. Cost is determined using the first-in, first-out method. Costs include the raw material consumed plus direct manufacturing costs (such as labor, utilities and supplies) as incurred and an applicable portion of manufacturing overhead.

Expendables Parts and Supplies. Inventories of expendable parts related to flight equipment, which cannot be economically repaired, reconditioned or reused after removal from the aircraft, are carried at moving average cost and charged to aircraft maintenance materials and outside repairs as consumed. An allowance for obsolescence is provided over the remaining useful life of the related fleet. We also provide allowances for parts identified as excess or obsolete to reduce the carrying costs to the lower of cost or net realizable value. These parts are estimated to have residual value of 5% of the original cost.

To the extent that we receive jet fuel for non-jet fuel products exchanged under buy/sell agreements, we account for these transactions as nonmonetary exchanges. We have recorded these nonmonetary exchanges at the carrying amount of the non-jet fuel products transferred within aircraft fuel and related taxes on the income statement.

Changes in fuel prices, interest rates and foreign currency exchange rates impact our results of operations. In an effort to manage our exposure to these risks, we may enter into derivative contracts and adjust our derivative portfolio as market conditions change. Our derivative contracts are recognized at fair value on our balance sheets and have net balances of $17 million and $1 million at December 31, 2021 and 2020, respectively.

Our long-lived lived assets, including flight equipment, which consists of aircraft and associated engines and parts, operating lease right-of-use ("ROU") assets and other long-lived assets, are recorded in property and equipment, net and operating lease right-of-use assets on our balance sheets. See Note 7, "Leases," for further information regarding our leases. The following table summarizes our property and equipment:


Property and equipment by classification
		December 31,
(in millions, except for estimated useful life)	Estimated Useful Life	2021		2020
Flight equipment	20-34 years	$	33,368	$	31,572
Ground property and equipment	3-40 years	7,758		6,387
Information technology-related assets	3-15 years	3,389		3,403
Flight and ground equipment under finance leases	Shorter of lease term or estimated useful life	2,052		1,795
Advance payments for equipment		853		883
Less: accumulated depreciation and amortization(1)		(18,671)		(17,511)
Total property and equipment, net		$	28,749	$	26,529

We record property and equipment at cost and depreciate or amortize these assets on a straight-line basis to their estimated residual values over their estimated useful lives. The estimated useful life for leasehold improvements is the shorter of lease term or estimated useful life. Depreciation and amortization expense related to our property and equipment was $2.0 billion, $2.3 billion and $2.6 billion for the years ended December 31, 2021, 2020 and 2019, respectively. Residual values for owned aircraft, engines, spare parts and simulators are generally 5% to 10% of cost.

We capitalize certain internal and external costs incurred to develop and implement software and amortize those costs over an estimated useful life of three to ten years. Included in the depreciation and amortization expense discussed above, we recorded $301 million, $304 million and $239 million for amortization of capitalized software for the years ended December 31, 2021, 2020 and 2019, respectively. The net book value of these assets, which are included in information technology-related assets above, totaled $876 million and $1.0 billion at December 31, 2021 and 2020, respectively.

We review flight equipment, ROU assets and other long-lived assets used in operations for impairment losses when events and circumstances indicate the assets may be impaired. Factors which could be indicators of impairment include, but are not limited to (1) a decision to permanently remove flight equipment or other long-lived assets from operations, (2) significant changes in the estimated useful life, (3) significant changes in projected cash flows, (4) permanent and significant declines in fleet fair values and (5) changes to the regulatory environment. For long-lived assets held for sale, we discontinue depreciation and record impairment losses when the carrying amount of these assets is greater than the fair value less the cost to sell.

To determine whether impairments exist for aircraft used in operations, we group assets at the fleet type level or at the contract level for aircraft operated by third-party regional carriers (i.e., the lowest level for which there are identifiable cash flows) and then estimate future cash flows based on projections of capacity, passenger mile yield, fuel and labor costs and other relevant factors. If an asset group is impaired, the impairment loss recognized is the amount by which the asset group's carrying amount exceeds its estimated fair value. We estimate aircraft fair values using published sources, appraisals and bids received from third parties, as available. Due to the impacts of the COVID-19 pandemic, we evaluated our fleet during 2020 and determined that only the fleet types discussed in Note 15, "Restructuring," were impaired, as the future cash flows from the operation of other fleet types through the respective retirement dates exceeded the carrying value. Due to the recovery in demand that we have experienced throughout 2021, we decided not to retire any additional aircraft and returned to service a majority of the aircraft that were temporarily parked in 2020. We recorded no further impairments during 2021. As we gained updated information during the year, we updated estimates to the 2020 fleet-related impairment charges and recorded adjustments of $19 million to certain of the restructuring charges during 2021.

We account for deferred income taxes under the liability method. We recognize deferred tax assets and liabilities based on the tax effects of temporary differences between the financial statement and tax basis of assets and liabilities, as measured by current enacted tax rates. Deferred tax assets and liabilities are net by jurisdiction and are recorded as noncurrent on the balance sheet.

A valuation allowance is recorded to reduce deferred tax assets when necessary. We periodically assess whether it is more likely than not that we will generate sufficient taxable income to realize our deferred income tax assets. We establish valuation allowances if it is more likely than not that we will be unable to realize our deferred income tax assets. In making this determination, we consider available positive and negative evidence and make certain assumptions. We consider, among other things, projected future taxable income, scheduled reversals of deferred tax liabilities, the overall business environment, our historical financial results and tax planning strategies. See Note 11, "Income Taxes," for further information on our deferred income taxes.

We have a purchasing card with American Express for the purpose of buying jet fuel and crude oil. The card carried a maximum credit limit of $1.1 billion as of December 31, 2021 and must be paid monthly. At both December 31, 2021 and 2020, we had $1.1 billion outstanding on this purchasing card and the activity was classified as a financing activity in our cash flows statement.

We record maintenance costs related to our mainline and regional fleets in aircraft maintenance materials and outside repairs and regional carrier expense, respectively. Maintenance costs are expensed as incurred, except for costs incurred under power-by-the-hour contracts, which are expensed based on actual hours flown. Power-by-the-hour contracts transfer certain risk to third-party service providers and fix the amount we pay per flight hour to the service provider in exchange for maintenance and repairs under a predefined maintenance program. Modifications that enhance the operating performance or extend the useful lives of airframes or engines are capitalized and amortized over the remaining estimated useful life of the asset or the remaining lease term, whichever is shorter.

We may purchase and retire carbon offsets and we expense the cost of carbon offsets upon retirement of the credits within aircraft fuel and related taxes on our income statement as these costs are related to our carbon emissions generated by our airline segment. The purchase of carbon offsets is included in operating activities on our cash flows statement. During 2021, we purchased and retired $95 million of carbon offsets, of which $30 million relates to 13 million metric tons of carbon emissions generated by our airline segment from March 1 to December 31, 2020 as well as $65 million which relates to a portion of 2021 carbon emissions generated by our airline segment.