ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
Dec. 31, 2020
Notes To Financial Statements [Abstract]
Principles of Consolidation	Summary of Significant Accounting Policies The financial statements and accompanying notes are prepared in accordance with accounting principles generally accepted in the United States of America ("GAAP"). The following is a description of our significant accounting policies. Principles of Consolidation The consolidated financial statements reflect the results of our operations, cash flows and financial position of our majority-owned or controlled subsidiaries. All intercompany accounts and transactions have been eliminated.
Equity and Cost Method Investments	Equity and Cost Method Investments Investments in unconsolidated entities over which we have significant influence are accounted for under the equity method of accounting. Under the equity method of accounting, the investment is initially recorded at cost, then our proportional share of the underlying net income or loss is recorded as Equity in net income from unconsolidated investments in our statement of operations with a corresponding increase or decrease to the carrying value of the investment. Distributions received from the investee reduce our carrying value of the investment and are recorded in the consolidated statements of cash flows using the cumulative earnings approach. These investments are evaluated for impairment if events or circumstances arise that indicate that the carrying amount of such assets may not be recoverable. There were no indicators of impairment related to our equity method investments for the years ended December 31, 2020 and 2019. Investments in entities over which we neither have significant influence nor control are accounted for using the cost method. Under the cost method, we record the investment at cost and recognize income for any dividends declared from distribution of the investments earnings. We review the cost method investments for impairment whenever events or changes in circumstances indicate that the carrying value may no longer be recoverable. We impair our cost method investments when we determine that there has been an “other-than temporary” decline in the investments' fair value compared to its carrying value. The fair value of the investment would then become the new cost basis of the investment. There were no indicators of impairment related to our cost method investments for the years ended December 31, 2020 and 2019.
Revenue Recognition	Revenue Recognition Our WtE projects generate revenue from three primary sources: 1) fees charged for operating facilities or for receiving waste for disposal (waste and service revenue); 2) the sale of electricity and/or steam (energy revenue); and 3) the sale of ferrous and non-ferrous metals that are recovered from the waste stream as part of the WtE process (recycled metals revenue). We may also generate other operating revenue from the construction, expansion or upgrade of a facility, when a public-sector client owns the facility. Our customers for waste services or facility operations are principally public-sector entities, though we also market disposal capacity at certain facilities to commercial customers. We also operate and/or have ownership positions in environmental services businesses, transfer stations and landfills (primarily for ash disposal) that are ancillary and complementary to our WtE projects and generate additional revenue from disposal or service fees. Revenue is allocated to the performance obligations in a contract on a relative standalone selling price basis. To the extent that we sell the good or service related to the performance obligation separately in the same market, the standalone selling price is the observable price that we sell the good or service separately in similar circumstances and to similar customers. The fees charged for our services are generally defined in our service agreements and vary based on contract-specific terms. Waste and Service Revenue Service Fee Service fee revenue is generated from the operations and maintenance services that we provide to owned and operated WtE facilities. We provide multiple waste disposal services aimed at operating and maintaining the facilities. Service fee revenue is generally based on an expected annual operating fee in relation to annual guaranteed waste processing and excess tonnage fees. The fees charged represent one performance obligation to operate and maintain each facility. Variable consideration primarily consists of fees earned for processing excess tonnage above a minimum specified in the contract. We act as the agent in contracts for the sale of energy and metals in service fee facilities that we operate and accordingly record revenues net for those contracts. Tip Fee Tip fees are generated from the sale of waste disposal services at WtE facilities that we own. We earn a per ton “tipping fee”, generally under long term contractual obligations with our host community and contractual obligations with municipal and commercial waste customers. The tipping fee is generally subject to an annual escalation. The performance obligation in these agreements is to provide waste disposal services for tons of acceptable waste. Revenue is recognized when the waste is delivered to the facility. Energy Sales Typical energy sales consist of: (a) electricity generation, (b) capacity and (c) steam. We primarily sell electricity either to utilities at contracted rates or at prevailing market rates in regional markets and in some cases, sell steam directly to industrial users. We sell a portion of electricity and other energy product outputs pursuant to contracts. As these contracts expire, we intend to sell an increasing portion of the energy output in competitive energy markets or pursuant to short-term contracts. Recycled Metals Revenue Recycled metals revenue represents the sale of recovered ferrous and non-ferrous metals to processors and end-users. The majority of our metals contracts are based on both an unspecified variable unit (i.e. tonnage) and variable forward market price index, while some contracts contain a fixed unit or fixed rate to form the basis of our overall transaction price. We recognize recycled metal revenue when control transfers to the customer. Other Operating Revenue (Construction) We generate additional revenue from the construction, expansion or upgrade of a facility, when a municipal client owns the facility and we provide the construction services. We generally use the cost incurred measure of progress for our construction contracts because it best depicts the transfer of control to the customer. Under the cost incurred measure of progress, the extent of progress towards completion is measured based on the ratio of costs incurred to date to the total estimated costs at completion of the performance obligation.
Plant Operating Expense	Plant Operating ExpensePlant operating expense includes facility employee costs, expense for materials and parts for facility scheduled and unscheduled maintenance and repair expense, which includes costs related to our internal maintenance team and non-facility employee costs. Plant operating expense also includes hauling and disposal expenses, fuel costs, chemicals and reagents, operating lease expense, and other facility operating related expense.
Pass Through Costs	Pass Through Costs Pass through costs are costs for which we receive a direct contractually committed reimbursement from the public sector client that sponsors an WtE project. These costs generally include utility charges, insurance premiums, ash residue transportation and disposal, and certain chemical costs. These costs are recorded net of public sector client reimbursements as a reduction to Plant operating expense in our consolidated statement of operations.
Income Taxes	Income Taxes Deferred income taxes are based on the difference between the financial reporting and tax basis of assets and liabilities. The deferred income tax provision represents the change during the reporting period in the deferred tax assets and deferred tax liabilities, net of the effect of acquisitions and dispositions. Deferred tax assets include tax losses and credit carryforwards and are reduced by a valuation allowance if, based on available evidence, it is more likely than not that some portion or all of the deferred tax assets will not be realized. We file a consolidated federal income tax return for each of the periods covered by the consolidated financial statements, which includes all eligible U.S. subsidiary companies. Foreign subsidiaries are taxed according to regulations existing in the countries in which they do business. Our federal consolidated income tax return also includes the taxable results of certain grantor trusts, which are excluded from our consolidated financial statements; however, certain related tax attributes are recorded in our consolidated financial statements since they are part of our federal tax return.
Share-Based Compensation	Stock-Based CompensationStock-based compensation awards to employees are accounted for as compensation expense based on their grant date fair values.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents include all cash balances and highly liquid investments having maturities of three months or less from the date of purchase. These short-term investments are stated at cost, which approximates fair value. Balances held by our international subsidiaries are not generally available for near-term liquidity in our domestic operations.
Restricted Funds Held in Trust	Restricted Funds Held in TrustRestricted funds held in trust are primarily amounts received and held by third party trustees relating to certain projects we own. We generally do not control these accounts and these funds may be used only for specified purposes. These funds include debt service reserves for payment of principal and interest on project debt. Revenue funds are comprised of deposits of revenue received with respect to projects prior to their disbursement. Other funds include escrowed debt proceeds, amounts held in trust for operations, maintenance, environmental obligations, operating lease reserves in accordance with agreements with our clients, and amounts held for future scheduled distributions. Such funds are invested principally in money market funds, bank deposits and U.S. treasury bills.
Accounts Receivable and Allowance for Doubtful Accounts	Receivables and Allowance for Doubtful Accounts Receivables consist of amounts due to us from normal business activities. Allowances for doubtful accounts are the estimated losses from the inability of customers to make required payments. For our trade receivables, we assess each counterparty’s ability to pay for service by conducting a credit review. The credit review considers the counterparty’s established credit rating or our assessment of the counterparty’s creditworthiness based on our analysis of their financial statements when a credit rating is not available. We monitor our ongoing credit exposure through active review of counterparty balances against contract terms and due dates. Our activities include timely account reconciliation, dispute resolution, payment confirmation and monitoring current economic conditions and future forecast of economic conditions, to the extent that they impact the credit loss determination and can be reasonably estimated. We regularly sell certain receivables on a revolving basis to third-party financial institutions up to an aggregate purchase limit (the "Receivables Purchase Agreement" or "RPA"). Transfers under the RPA meet the requirements to be accounted for as sales in accordance with the Transfers and Servicing topic of Financial Accounting Standards Board (“FASB”) Accounting Standards Codification. We receive a discounted purchase price for each receivable sold under the RPA and will continue to service and administer the subject receivables. For additional information, see Note 10. Accounts Receivable Securitization.
Property, Plant and Equipment	Property, Plant and Equipment, net Property, plant, and equipment acquired in business acquisitions is recorded at our estimate of fair value on the date of the acquisition. Additions, improvements and major expenditures are capitalized if they increase the original capacity or extend the remaining useful life of the original asset more than one year. Maintenance repairs and minor expenditures are expensed in the period incurred. Depreciation is computed using the straight-line method over the estimated useful lives of the assets, which generally range from three years for computer equipment to 50 years for certain infrastructure components of WtE facilities. Property, plant and equipment at our service fee operated facilities are not recognized on our balance sheet and any additions, improvements and major expenditures for which we are responsible at our service fee operated facilities are expensed in the period incurred. Our leasehold improvements are depreciated over the life of the lease term or the asset life, whichever is shorter. Upon retirement or disposal of assets, the cost and related accumulated depreciation are removed from the consolidated balance sheets and any gain or loss is reflected in the consolidated statements of operations.
Property, Plant and Equipment, Impairment	Property, plant and equipment is evaluated for impairment whenever events or changes in circumstances indicate their carrying value may not be recoverable over their estimated useful life. In reviewing for recoverability, we compare the carrying amount of the relevant assets to their estimated undiscounted future cash flows. When the estimated undiscounted future cash flows are less than the assets carrying amount, the carrying amount is compared to the assets fair value. If the assets fair value is less than the carrying amount an impairment charge is recognized to reduce the assets carrying amount to its fair value.
Asset Retirement Obligations	We recognize a liability for asset retirement obligations when it is incurred, which is generally upon acquisition, construction, or development. Our liabilities include closure and post-closure costs for landfill cells and site restoration for certain WtE and power producing sites. We principally determine the liability using internal estimates of the costs using current information, assumptions, and interest rates, but also use independent appraisals as appropriate to estimate costs. When a new liability for asset retirement obligation is recorded, we capitalize the cost of the liability by increasing the carrying amount of the related long-lived asset. The liability is accreted to its present value each period and the capitalized cost is depreciated over the useful life of the related asset. We recognize period-to-period changes in the liability resulting from revisions to the timing or the amount of the original estimate of the undiscounted cash flows.
Intangible Assets and Liabilities	Intangible Assets and LiabilitiesOur waste, service and energy contracts are intangible assets related to long-term operating contracts at acquired facilities. These intangible assets and liabilities and other finite intangible assets, are recorded at their estimated fair market values upon acquisition based primarily upon discounted cash flows in accordance with accounting standards related to business combinations.
Impairment or Disposal of Long-Lived Assets, Including Intangible Assets	Intangible assets with finite lives are evaluated for impairment whenever events or changes in circumstances indicate their carrying value may not be recoverable over their estimated useful life. In reviewing for recoverability, we compare the carrying amount of the relevant assets to their estimated undiscounted future cash flows. When the estimated undiscounted future cash flows are less than the assets carrying amount, the carrying amount is compared to the assets fair value. If the assets fair value is less than the carrying amount an impairment charge is recognized to reduce the assets carrying amount to its fair value. For the years ended December 31, 2020, 2019 and 2018, we recognized an impairment on our intangible assets of zero, zero and $22 million, respectively.
Goodwill	GoodwillGoodwill is the excess of our purchase price over the fair value of the net assets of acquired businesses. We do not amortize goodwill, but we assess our goodwill for impairment at least annually. The evaluation of goodwill requires the use of estimates of future cash flows to determine the estimated fair value of the reporting unit. All goodwill is related to our one reportable segment, which is comprised of two reporting units, North America WtE and CES. A reporting unit is defined as an operating segment or a component of an operating segment to the extent discrete financial information is available that is reviewed by segment management which has been determined to be one level below our chief operating decision maker. If the carrying value of the reporting unit exceeds the fair value, an impairment charge is recognized to reduce the carrying value to the fair value.
Business Combinations	usiness CombinationsWe recognize the assets acquired and liabilities assumed in a business combination at fair value including any noncontrolling interest of the acquired entity; recognize any goodwill acquired; establish the acquisition-date fair value based on the highest and best use by market participants for the asset as the measurement objective; and disclose information needed to evaluate and understand the nature and financial effect of the business combination. We expense transaction costs directly associated to the acquisition as incurred; capitalize in-process research and development costs, if any; and record a liability for contingent consideration at the measurement date with subsequent remeasurement recognized in the results of operations. Any costs for business restructuring and exit activities related to the acquired company are included in the post-combination results of operations. Tax adjustments related to previously recorded business combinations, if any, are recognized in the results of operations.
Derivative Instruments	Derivative InstrumentsWe recognize derivative instruments on the balance sheet at their fair value. We have entered into swap agreements with various financial institutions to hedge our exposure to energy price risk and interest rate risk. Changes in the fair value of the energy derivatives and the interest rate swap are recognized as a component of AOCI. For additional information, see Note 15. Derivative Instruments.
Foreign Currency Translation	Foreign Currency Translation For foreign operations, assets and liabilities are translated at year-end exchange rates and revenue and expense are translated at the average exchange rates during the year. Unrealized gains and losses resulting from foreign currency translation are included in the consolidated statements of equity as a component of AOCI. Currency transaction gains and losses are recorded in other operating expense in the consolidated statements of operations.
Pension and Postretirement Benefit Obligations	Defined Contribution Plans Substantially all of our employees in the U.S. are eligible to participate in the defined contribution plans we sponsor. The defined contribution plans allow employees to contribute a portion of their compensation on a pre-tax basis in accordance with specified guidelines. We match a percentage of employee contributions up to certain limits. We also provide a company contribution to the defined contribution plans for eligible employees. Our costs related to defined contribution plans were $20 million, $20 million and $18 million for the years ended December 31, 2020, 2019 and 2018, respectively.
Share Repurchases	Share RepurchasesUnder our share repurchase program, common stock repurchases may be made, from time to time, in the open market, in privately negotiated transactions, or by other available methods, at management’s discretion and in accordance with applicable federal securities laws. The timing and amounts of any repurchases will depend on many factors, including our capital structure, the market price of our common stock and overall market conditions, and whether any restrictions then exist under our policies relating to trading in compliance with securities laws. Purchase price over par value for share repurchases are allocated to additional paid-in capital up to the weighted average amount per share recorded at the time of initial issuance of our common stock, with any excess recorded as a reduction to retained earnings.
Use of Estimates	Use of Estimates The preparation of financial statements requires us to make estimates and assumptions that affect the reported amounts of assets or liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expense during the reporting period. Actual results could differ from those estimates. Significant estimates include: useful lives of long-lived assets, asset retirement obligations, construction expense estimates, unbilled service receivables, fair value of financial instruments, fair value of the reporting units for goodwill impairment analysis, fair value of long-lived assets for impairment analysis, renewable energy credits, stock-based compensation, cash flows and taxable income from future operations, valuation allowance for deferred taxes, liabilities related to uncertain tax positions, allowances for uncollectible receivables, and liabilities related to employee medical benefit obligations and certain litigation.
New Accounting Pronouncements, Policy [Policy Text Block]	Accounting Pronouncements Recently Adopted In August 2019, the FASB issued Accounting Standards Update (“ASU”) ASU 2018-15, Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract. The amendments in this update align the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. We adopted this guidance on January 1, 2020 on a prospective basis. The adoption of this guidance did not have a material impact on our consolidated financial statements. In June 2016, the FASB issued ASU 2016-13, “Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments,” which amends the impairment model to utilize an expected loss methodology in place of the incurred loss methodology for financial instruments and off balance sheet credit exposures. The amendment requires entities to consider a broader range of information to estimate expected credit losses, which may result in earlier recognition of losses. We adopted this guidance on January 1, 2020 using a modified retrospective approach. The adoption of this guidance did not have a material impact on our consolidated financial statements.
Earnings Per Share	EPS We calculate basic EPS using net earnings for the period and the weighted average number of outstanding shares of our common stock, par value $0.10 per share, during the period. Diluted earnings per share computations, as calculated under the treasury stock method, include the weighted average number of shares of additional outstanding common stock issuable for stock options, restricted stock awards and restricted stock units whether or not currently exercisable. Diluted earnings per share does not include securities if their effect was anti-dilutive.
Fair Value Measurements	Fair Value Measurements Authoritative guidance associated with fair value measurements provides a framework for measuring fair value and establishes a fair value hierarchy that prioritizes the inputs used to measure fair value, giving the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 inputs), then significant other observable inputs (Level 2 inputs) and the lowest priority to significant unobservable inputs (Level 3 inputs). The following methods and assumptions were used to estimate the fair value of each class of financial instruments: •For marketable securities, the carrying value of these amounts is a reasonable estimate of their fair value. •Fair values for long-term debt and project debt are determined using quoted market prices (Level 1). •The fair value of our floating to fixed rate interest rate swaps is determined using discounted cash flow valuation methodologies that apply the appropriate forward floating rate curve observable in the market to the contractual terms of our swap agreements. The fair value of the interest rate swaps is adjusted to reflect counterparty risk of non-performance and is based on the counterparty’s credit spread in the credit derivatives market. •The fair values of our energy hedges were determined using the spread between our fixed price and the forward curve information available within the market. The estimated fair value amounts have been determined using available market information and appropriate valuation methodologies. However, considerable judgment is required in interpreting market data to develop estimates of fair value. Accordingly, the estimates presented herein are not necessarily indicative of the amounts that we would realize in a current market exchange and are based on pertinent information available to us as of December 31, 2020. Such amounts have not been comprehensively revalued for purposes of these financial statements and current estimates of fair value may differ significantly from the amounts presented herein.
Leases	ROU assets represent our right to use an underlying asset for the lease term and lease liabilities represent our obligation to make lease payments arising from the lease. ROU assets and liabilities are recognized at the lease commencement date based on the estimated present value of lease payments over the lease term. We determine if an arrangement contains a lease at inception. Our leases consist of leaseholds on WtE facilities, land, trucks and automobiles, office space, and machinery and equipment. We utilized a portfolio approach in determining our discount rate. The portfolio approach takes into consideration the range of the term, the range of the lease payments, the category of the underlying asset and our estimated incremental borrowing rate, which is derived from information available at the lease commencement date, in determining the present value of lease payments. We also give consideration to our recent debt issuances as well as publicly available data for instruments with similar characteristics when calculating our incremental borrowing rates. ASC 842 provides that leases with a term of 12 months or less are not recorded on the balance sheet. The guidance also provides practical expedients whereby we have elected to not record a right of use asset or right of use liability for leases with an asset balance that would be considered immaterial. Furthermore, non-lease components are not separated from lease components and instead we account for each separate lease component and non-lease component associated with that lease as a single lease component. We recognize lease expense for these leases on a straight-line basis over the lease term. Our lease term includes options to extend the lease when it is reasonably certain that we will exercise that option. We recognize variable lease payments in the period in which the obligation for those payments is incurred. Variable lease payments that depend on an index or a rate are initially measured using the index or rate at the commencement date, otherwise variable lease payments are recognized in the period incurred.

ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)

12 Months Ended

Dec. 31, 2020

Notes To Financial Statements [Abstract]

Summary of Significant Accounting Policies

The financial statements and accompanying notes are prepared in accordance with accounting principles generally accepted in the United States of America ("GAAP"). The following is a description of our significant accounting policies.

Principles of Consolidation

The consolidated financial statements reflect the results of our operations, cash flows and financial position of our majority-owned or controlled subsidiaries. All intercompany accounts and transactions have been eliminated.

Equity and Cost Method Investments

Investments in unconsolidated entities over which we have significant influence are accounted for under the equity method of accounting. Under the equity method of accounting, the investment is initially recorded at cost, then our proportional share of the underlying net income or loss is recorded as Equity in net income from unconsolidated investments in our statement of operations with a corresponding increase or decrease to the carrying value of the investment. Distributions received from the investee reduce our carrying value of the investment and are recorded in the consolidated statements of cash flows using the cumulative earnings approach. These investments are evaluated for impairment if events or circumstances arise that indicate that the carrying amount of such assets may not be recoverable. There were no indicators of impairment related to our equity method investments for the years ended December 31, 2020 and 2019.

Investments in entities over which we neither have significant influence nor control are accounted for using the cost method. Under the cost method, we record the investment at cost and recognize income for any dividends declared from distribution of the investments earnings. We review the cost method investments for impairment whenever events or changes in circumstances indicate that the carrying value may no longer be recoverable. We impair our cost method investments when we determine that there has been an “other-than temporary” decline in the investments' fair value compared to its carrying value. The fair value of the investment would then become the new cost basis of the investment. There were no indicators of impairment related to our cost method investments for the years ended December 31, 2020 and 2019.

Revenue Recognition

Our WtE projects generate revenue from three primary sources: 1) fees charged for operating facilities or for receiving waste for disposal (waste and service revenue); 2) the sale of electricity and/or steam (energy revenue); and 3) the sale of ferrous and non-ferrous metals that are recovered from the waste stream as part of the WtE process (recycled metals revenue). We may also generate other operating revenue from the construction, expansion or upgrade of a facility, when a public-sector client owns the facility. Our customers for waste services or facility operations are principally public-sector entities, though we also market disposal capacity at certain facilities to commercial customers.

We also operate and/or have ownership positions in environmental services businesses, transfer stations and landfills (primarily for ash disposal) that are ancillary and complementary to our WtE projects and generate additional revenue from disposal or service fees.

Revenue is allocated to the performance obligations in a contract on a relative standalone selling price basis. To the extent that we sell the good or service related to the performance obligation separately in the same market, the standalone selling price is the observable price that we sell the good or service separately in similar circumstances and to similar customers. The fees charged for our services are generally defined in our service agreements and vary based on contract-specific terms.

Waste and Service Revenue

Service Fee

Service fee revenue is generated from the operations and maintenance services that we provide to owned and operated WtE facilities. We provide multiple waste disposal services aimed at operating and maintaining the facilities. Service fee revenue is generally based on an expected annual operating fee in relation to annual guaranteed waste processing and excess tonnage fees. The fees charged represent one performance obligation to operate and maintain each facility. Variable consideration primarily consists of fees earned for processing excess tonnage above a minimum specified in the contract. We act as the agent in contracts for the sale of energy and metals in service fee facilities that we operate and accordingly record revenues net for those contracts.

Tip Fee

Tip fees are generated from the sale of waste disposal services at WtE facilities that we own. We earn a per ton “tipping fee”, generally under long term contractual obligations with our host community and contractual obligations with municipal and commercial waste customers. The tipping fee is generally subject to an annual escalation. The performance obligation in these agreements is to provide waste disposal services for tons of acceptable waste. Revenue is recognized when the waste is delivered to the facility.

Energy Sales

Typical energy sales consist of: (a) electricity generation, (b) capacity and (c) steam. We primarily sell electricity either to utilities at contracted rates or at prevailing market rates in regional markets and in some cases, sell steam directly to industrial users. We sell a portion of electricity and other energy product outputs pursuant to contracts. As these contracts expire, we intend to sell an increasing portion of the energy output in competitive energy markets or pursuant to short-term contracts.

Recycled Metals Revenue

Recycled metals revenue represents the sale of recovered ferrous and non-ferrous metals to processors and end-users. The majority of our metals contracts are based on both an unspecified variable unit (i.e. tonnage) and variable forward market price

index, while some contracts contain a fixed unit or fixed rate to form the basis of our overall transaction price. We recognize recycled metal revenue when control transfers to the customer.

Other Operating Revenue (Construction)

We generate additional revenue from the construction, expansion or upgrade of a facility, when a municipal client owns the facility and we provide the construction services. We generally use the cost incurred measure of progress for our construction contracts because it best depicts the transfer of control to the customer. Under the cost incurred measure of progress, the extent of progress towards completion is measured based on the ratio of costs incurred to date to the total estimated costs at completion of the performance obligation.

Plant Operating Expense

Plant Operating ExpensePlant operating expense includes facility employee costs, expense for materials and parts for facility scheduled and unscheduled maintenance and repair expense, which includes costs related to our internal maintenance team and non-facility employee costs. Plant operating expense also includes hauling and disposal expenses, fuel costs, chemicals and reagents, operating lease expense, and other facility operating related expense.

Pass Through Costs

Pass through costs are costs for which we receive a direct contractually committed reimbursement from the public sector client that sponsors an WtE project. These costs generally include utility charges, insurance premiums, ash residue transportation and disposal, and certain chemical costs. These costs are recorded net of public sector client reimbursements as a reduction to Plant operating expense in our consolidated statement of operations.

Income Taxes

Deferred income taxes are based on the difference between the financial reporting and tax basis of assets and liabilities. The deferred income tax provision represents the change during the reporting period in the deferred tax assets and deferred tax liabilities, net of the effect of acquisitions and dispositions. Deferred tax assets include tax losses and credit carryforwards and are reduced by a valuation allowance if, based on available evidence, it is more likely than not that some portion or all of the deferred tax assets will not be realized.

We file a consolidated federal income tax return for each of the periods covered by the consolidated financial statements, which includes all eligible U.S. subsidiary companies. Foreign subsidiaries are taxed according to regulations existing in the countries in which they do business. Our federal consolidated income tax return also includes the taxable results of certain grantor trusts, which are excluded from our consolidated financial statements; however, certain related tax attributes are recorded in our consolidated financial statements since they are part of our federal tax return.

Share-Based Compensation

Stock-Based CompensationStock-based compensation awards to employees are accounted for as compensation expense based on their grant date fair values.

Cash and Cash Equivalents

Cash and cash equivalents include all cash balances and highly liquid investments having maturities of three months or less from the date of purchase. These short-term investments are stated at cost, which approximates fair value. Balances held by our international subsidiaries are not generally available for near-term liquidity in our domestic operations.

Restricted Funds Held in Trust

Restricted Funds Held in TrustRestricted funds held in trust are primarily amounts received and held by third party trustees relating to certain projects we own. We generally do not control these accounts and these funds may be used only for specified purposes. These funds include debt service reserves for payment of principal and interest on project debt. Revenue funds are comprised of deposits of revenue received with respect to projects prior to their disbursement. Other funds include escrowed debt proceeds, amounts held in trust for operations, maintenance, environmental obligations, operating lease reserves in accordance with agreements with our clients, and amounts held for future scheduled distributions. Such funds are invested principally in money market funds, bank deposits and U.S. treasury bills.

Accounts Receivable and Allowance for Doubtful Accounts

Receivables and Allowance for Doubtful Accounts

Receivables consist of amounts due to us from normal business activities. Allowances for doubtful accounts are the estimated losses from the inability of customers to make required payments.

For our trade receivables, we assess each counterparty’s ability to pay for service by conducting a credit review. The credit review considers the counterparty’s established credit rating or our assessment of the counterparty’s creditworthiness based on our analysis of their financial statements when a credit rating is not available.

We monitor our ongoing credit exposure through active review of counterparty balances against contract terms and due dates. Our activities include timely account reconciliation, dispute resolution, payment confirmation and monitoring current economic conditions and future forecast of economic conditions, to the extent that they impact the credit loss determination and can be reasonably estimated.

We regularly sell certain receivables on a revolving basis to third-party financial institutions up to an aggregate purchase limit (the "Receivables Purchase Agreement" or "RPA"). Transfers under the RPA meet the requirements to be accounted for as sales in accordance with the Transfers and Servicing topic of Financial Accounting Standards Board (“FASB”) Accounting Standards Codification. We receive a discounted purchase price for each receivable sold under the RPA and will continue to service and administer the subject receivables. For additional information, see Note 10. Accounts Receivable Securitization.

Property, Plant and Equipment

Property, Plant and Equipment, net

Property, plant, and equipment acquired in business acquisitions is recorded at our estimate of fair value on the date of the acquisition. Additions, improvements and major expenditures are capitalized if they increase the original capacity or extend the remaining useful life of the original asset more than one year. Maintenance repairs and minor expenditures are expensed in the period incurred. Depreciation is computed using the straight-line method over the estimated useful lives of the assets, which generally range from three years for computer equipment to 50 years for certain infrastructure components of WtE facilities. Property, plant and equipment at our service fee operated facilities are not recognized on our balance sheet and any additions, improvements and major expenditures for which we are responsible at our service fee operated facilities are expensed in the period incurred. Our leasehold improvements are depreciated over the life of the lease term or the asset life, whichever is shorter. Upon retirement or disposal of assets, the cost and related accumulated depreciation are removed from the consolidated balance sheets and any gain or loss is reflected in the consolidated statements of operations.

Property, Plant and Equipment, Impairment

Property, plant and equipment is evaluated for impairment whenever events or changes in circumstances indicate their carrying value may not be recoverable over their estimated useful life. In reviewing for recoverability, we compare the carrying amount of the relevant assets to their estimated undiscounted future cash flows. When the estimated undiscounted future cash flows are less than the assets carrying amount, the carrying amount is compared to the assets fair value. If the assets fair value is less than the carrying amount an impairment charge is recognized to reduce the assets carrying amount to its fair value.

Asset Retirement Obligations

We recognize a liability for asset retirement obligations when it is incurred, which is generally upon acquisition, construction, or development. Our liabilities include closure and post-closure costs for landfill cells and site restoration for certain WtE and power producing sites. We principally determine the liability using internal estimates of the costs using current information, assumptions, and interest rates, but also use independent appraisals as appropriate to estimate costs. When a new liability for asset retirement obligation is recorded, we capitalize the cost of the liability by increasing the carrying amount of the related long-lived asset. The liability is accreted to its present value each period and the capitalized cost is depreciated over the useful life of the related asset. We recognize period-to-period changes in the liability resulting from revisions to the timing or the amount of the original estimate of the undiscounted cash flows.

Intangible Assets and Liabilities

Intangible Assets and LiabilitiesOur waste, service and energy contracts are intangible assets related to long-term operating contracts at acquired facilities. These intangible assets and liabilities and other finite intangible assets, are recorded at their estimated fair market values upon acquisition based primarily upon discounted cash flows in accordance with accounting standards related to business combinations.

Impairment or Disposal of Long-Lived Assets, Including Intangible Assets

Intangible assets with finite lives are evaluated for impairment whenever events or changes in circumstances indicate their carrying value may not be recoverable over their estimated useful life. In reviewing for recoverability, we compare the carrying amount of the relevant assets to their estimated undiscounted future cash flows. When the estimated undiscounted future cash flows are less than the assets carrying amount, the carrying amount is compared to the assets fair value. If the assets fair value is less than the carrying amount an impairment charge is recognized to reduce the assets carrying amount to its fair value. For the years ended December 31, 2020, 2019 and 2018, we recognized an impairment on our intangible assets of zero, zero and $22 million, respectively.

Goodwill

GoodwillGoodwill is the excess of our purchase price over the fair value of the net assets of acquired businesses. We do not amortize goodwill, but we assess our goodwill for impairment at least annually. The evaluation of goodwill requires the use of estimates of future cash flows to determine the estimated fair value of the reporting unit. All goodwill is related to our one reportable segment, which is comprised of two reporting units, North America WtE and CES. A reporting unit is defined as an operating segment or a component of an operating segment to the extent discrete financial information is available that is reviewed by segment management which has been determined to be one level below our chief operating decision maker. If the carrying value of the reporting unit exceeds the fair value, an impairment charge is recognized to reduce the carrying value to the fair value.

Business Combinations

usiness CombinationsWe recognize the assets acquired and liabilities assumed in a business combination at fair value including any noncontrolling interest of the acquired entity; recognize any goodwill acquired; establish the acquisition-date fair value based on the highest and best use by market participants for the asset as the measurement objective; and disclose information needed to evaluate and understand the nature and financial effect of the business combination. We expense transaction costs directly associated to the acquisition as incurred; capitalize in-process research and development costs, if any; and record a liability for contingent consideration at the measurement date with subsequent remeasurement recognized in the results of operations. Any costs for business restructuring and exit activities related to the acquired company are included in the post-combination results of operations. Tax adjustments related to previously recorded business combinations, if any, are recognized in the results of operations.

Derivative Instruments

Derivative InstrumentsWe recognize derivative instruments on the balance sheet at their fair value. We have entered into swap agreements with various financial institutions to hedge our exposure to energy price risk and interest rate risk. Changes in the fair value of the energy derivatives and the interest rate swap are recognized as a component of AOCI. For additional information, see Note 15. Derivative Instruments.

Foreign Currency Translation

For foreign operations, assets and liabilities are translated at year-end exchange rates and revenue and expense are translated at the average exchange rates during the year. Unrealized gains and losses resulting from foreign currency translation are included in the consolidated statements of equity as a component of AOCI. Currency transaction gains and losses are recorded in other operating expense in the consolidated statements of operations.

Pension and Postretirement Benefit Obligations

Defined Contribution Plans

Substantially all of our employees in the U.S. are eligible to participate in the defined contribution plans we sponsor. The defined contribution plans allow employees to contribute a portion of their compensation on a pre-tax basis in accordance with specified guidelines. We match a percentage of employee contributions up to certain limits. We also provide a company contribution to the defined contribution plans for eligible employees. Our costs related to defined contribution plans were $20 million, $20 million and $18 million for the years ended December 31, 2020, 2019 and 2018, respectively.

Share Repurchases

Share RepurchasesUnder our share repurchase program, common stock repurchases may be made, from time to time, in the open market, in privately negotiated transactions, or by other available methods, at management’s discretion and in accordance with applicable federal securities laws. The timing and amounts of any repurchases will depend on many factors, including our capital structure, the market price of our common stock and overall market conditions, and whether any restrictions then exist under our policies relating to trading in compliance with securities laws. Purchase price over par value for share repurchases are allocated to additional paid-in capital up to the weighted average amount per share recorded at the time of initial issuance of our common stock, with any excess recorded as a reduction to retained earnings.

Use of Estimates

The preparation of financial statements requires us to make estimates and assumptions that affect the reported amounts of assets or liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expense during the reporting period. Actual results could differ from those estimates. Significant estimates include: useful lives of long-lived assets, asset retirement obligations, construction expense estimates,

unbilled service receivables, fair value of financial instruments, fair value of the reporting units for goodwill impairment analysis, fair value of long-lived assets for impairment analysis, renewable energy credits, stock-based compensation, cash flows and taxable income from future operations, valuation allowance for deferred taxes, liabilities related to uncertain tax positions, allowances for uncollectible receivables, and liabilities related to employee medical benefit obligations and certain litigation.

New Accounting Pronouncements, Policy [Policy Text Block]

Accounting Pronouncements Recently Adopted

In August 2019, the FASB issued Accounting Standards Update (“ASU”) ASU 2018-15, Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract. The amendments in this update align the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. We adopted this guidance on January 1, 2020 on a prospective basis. The adoption of this guidance did not have a material impact on our consolidated financial statements.

In June 2016, the FASB issued ASU 2016-13, “Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments,” which amends the impairment model to utilize an expected loss methodology in place of the incurred loss methodology for financial instruments and off balance sheet credit exposures. The amendment requires entities to consider a broader range of information to estimate expected credit losses, which may result in earlier recognition of losses. We adopted this guidance on January 1, 2020 using a modified retrospective approach. The adoption of this guidance did not have a material impact on our consolidated financial statements.

Earnings Per Share

EPS

We calculate basic EPS using net earnings for the period and the weighted average number of outstanding shares of our common stock, par value $0.10 per share, during the period. Diluted earnings per share computations, as calculated under the treasury stock method, include the weighted average number of shares of additional outstanding common stock issuable for stock options, restricted stock awards and restricted stock units whether or not currently exercisable. Diluted earnings per share does not include securities if their effect was anti-dilutive.

Fair Value Measurements

Authoritative guidance associated with fair value measurements provides a framework for measuring fair value and establishes a fair value hierarchy that prioritizes the inputs used to measure fair value, giving the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 inputs), then significant other observable inputs (Level 2 inputs) and the lowest priority to significant unobservable inputs (Level 3 inputs). The following methods and assumptions were used to estimate the fair value of each class of financial instruments:

•For marketable securities, the carrying value of these amounts is a reasonable estimate of their fair value.

•Fair values for long-term debt and project debt are determined using quoted market prices (Level 1).

•The fair value of our floating to fixed rate interest rate swaps is determined using discounted cash flow valuation methodologies that apply the appropriate forward floating rate curve observable in the market to the contractual terms of our swap agreements. The fair value of the interest rate swaps is adjusted to reflect counterparty risk of non-performance and is based on the counterparty’s credit spread in the credit derivatives market.

•The fair values of our energy hedges were determined using the spread between our fixed price and the forward curve information available within the market.

The estimated fair value amounts have been determined using available market information and appropriate valuation methodologies. However, considerable judgment is required in interpreting market data to develop estimates of fair value. Accordingly, the estimates presented herein are not necessarily indicative of the amounts that we would realize in a current market exchange and are based on pertinent information available to us as of December 31, 2020. Such amounts have not been comprehensively revalued for purposes of these financial statements and current estimates of fair value may differ significantly from the amounts presented herein.

Leases

ROU assets represent our right to use an underlying asset for the lease term and lease liabilities represent our obligation to make lease payments arising from the lease. ROU assets and liabilities are recognized at the lease commencement date based on the estimated present value of lease payments over the lease term. We determine if an arrangement contains a lease at inception.

Our leases consist of leaseholds on WtE facilities, land, trucks and automobiles, office space, and machinery and equipment. We utilized a portfolio approach in determining our discount rate. The portfolio approach takes into consideration the range of the term, the range of the lease payments, the category of the underlying asset and our estimated incremental borrowing rate, which is derived from information available at the lease commencement date, in determining the present value of lease payments. We also give consideration to our recent debt issuances as well as publicly available data for instruments with similar characteristics when calculating our incremental borrowing rates.

ASC 842 provides that leases with a term of 12 months or less are not recorded on the balance sheet. The guidance also provides practical expedients whereby we have elected to not record a right of use asset or right of use liability for leases with an asset balance that would be considered immaterial. Furthermore, non-lease components are not separated from lease components and instead we account for each separate lease component and non-lease component associated with that lease as a single lease component.

We recognize lease expense for these leases on a straight-line basis over the lease term. Our lease term includes options to extend the lease when it is reasonably certain that we will exercise that option. We recognize variable lease payments in the period in which the obligation for those payments is incurred. Variable lease payments that depend on an index or a rate are initially measured using the index or rate at the commencement date, otherwise variable lease payments are recognized in the period incurred.