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 generally accepted accounting principles in the U.S. ("GAAP"). We are not the primary beneficiary of, nor do we have a controlling financial interest in, any variable interest entity. Accordingly, we have not consolidated any variable interest entity.

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, 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").

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.

Fair Value of Equity Investments. In June 2022, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") No. 2022-03, "Fair Value Measurement (Topic 820): Fair Value Measurement of Equity Securities Subject to Contractual Sale Restrictions." Under this standard, a contractual restriction on the sale of an equity security is not considered in measuring the security's fair value. The standard also requires certain disclosures for equity securities that are subject to contractual restrictions. The ASU becomes effective January 1, 2024, however we early adopted this standard as of December 31, 2023. The new standard does not impact the valuation of our equity investments, but we have included the newly required disclosures related to the contractual sale restrictions associated with our investment in Wheels Up Experience Inc. ("Wheels Up"). See Note 4, "Investments," for additional details.

Segment Reporting. In November 2023, the FASB issued ASU No. 2023-07, "Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures." This standard requires disclosure of significant segment expenses and other segment items by reportable segment. This ASU becomes effective for annual periods beginning in 2024 and interim periods in 2025. We are assessing the impact of this ASU and upon adoption expect that any impact would be limited to additional segment expense disclosures in the footnotes to our Consolidated Financial Statements.

Income Taxes. In December 2023, the FASB issued ASU No. 2023-09, "Income Taxes (Topic 740): Improvements to Income Tax Disclosures." This standard enhances disclosures related to income taxes, including the rate reconciliation and information on income taxes paid. This ASU becomes effective January 1, 2025. We are assessing the impact of this ASU and upon adoption may be required to include certain additional disclosures in the footnotes to our Consolidated Financial Statements.

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 and are stated at fair value. 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 in debt securities purchased prior to October 1, 2022 are classified as fair value investments under the fair value option and unrealized gains and losses are recorded in non-operating expense. Our short-term investments in debt securities purchased on or after October 1, 2022 are classified as available-for-sale investments and are stated at fair value with unrealized gains and losses recorded in accumulated other comprehensive income/(loss) ("AOCI"). Realized gains and losses on these investments are recorded in non-operating expense.

The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the Consolidated Balance Sheets ("balance sheets") that sum to the total of the same such amounts shown within the Consolidated Statements of Cash Flows ("cash flows statement").


Reconciliation of cash, cash equivalents and restricted cash
	December 31,
(in millions)	2023		2022		2021
Current assets:
Cash and cash equivalents	$	2,741	$	3,266	$	7,933
Restricted cash included in prepaid expenses and other	199		138		163
Noncurrent assets:
Restricted cash included in other noncurrent assets	455		69		473
Total cash, cash equivalents and restricted cash	$	3,395	$	3,473	$	8,569

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 exchanges 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 had net balances of $5 million and $47 million at December 31, 2023 and 2022, respectively. See Note 3, "Fair Value Measurements," for further information regarding our derivative contracts.

Our long-lived lived assets include property and equipment, net and operating lease right-of-use ("ROU") 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	2023		2022
Flight equipment(1)	25-34 years	$	40,976	$	38,091
Ground property and equipment	3-40 years	9,986		8,996
Information technology-related assets	3-15 years	3,307		3,375
Flight and ground equipment under finance leases	Shorter of lease term or estimated useful life	1,862		1,950
Advance payments for equipment		1,062		1,067
Less: accumulated depreciation and amortization(2)		(21,707)		(20,370)
Total property and equipment, net		$	35,486	$	33,109

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 $2.3 billion, $2.1 billion and $2.0 billion for the years ended December 31, 2023, 2022 and 2021, 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 fifteen years. Included in the depreciation and amortization expense discussed above, we recorded $340 million, $307 million and $301 million for amortization of capitalized software for the years ended December 31, 2023, 2022 and 2021, respectively. The net book value of these assets, which are included in information technology-related assets above, totaled $932 million and $891 million at December 31, 2023 and 2022, 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.

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 sheets.

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, 2023 and must be paid monthly. At both December 31, 2023 and 2022, 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 periodically receive credits in connection with the acquisition of aircraft and engines. These credits are deferred until the aircraft and engines are delivered, and then applied as a reduction to the cost of the related equipment.

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 or per flight cycle 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 expense advertising costs in passenger commissions and other selling expenses in the year the advertising first takes place. Advertising expense was $347 million, $302 million and $198 million for the years ended December 31, 2023, 2022 and 2021, respectively.