| Significant Accounting Policies (Policy) | 12 Months Ended |
| Dec. 31, 2020 |
| Significant Accounting Policies [Line Items] | |
| Principles of Consolidation | Principles of Consolidation: CMS Energy and Consumers prepare their consolidated financial statements in conformity with GAAP. CMS Energy’s consolidated financial statements comprise CMS Energy, Consumers, CMS Enterprises, EnerBank, and all other entities in which CMS Energy has a controlling financial interest or is the primary beneficiary. Consumers’ consolidated financial statements comprise Consumers and all other entities in which it has a controlling financial interest or is the primary beneficiary. CMS Energy uses the equity method of accounting for investments in companies and partnerships that are not consolidated, where they have significant influence over operations and financial policies but are not the primary beneficiary. CMS Energy and Consumers eliminate intercompany transactions and balances. |
| Use of Estimates | Use of Estimates: CMS Energy and Consumers are required to make estimates using assumptions that may affect reported amounts and disclosures. Actual results could differ from those estimates. |
| Contingencies | Contingencies: CMS Energy and Consumers record estimated liabilities for contingencies on their consolidated financial statements when it is probable that a liability has been incurred and when the amount of loss can be reasonably estimated. For environmental remediation projects in which the timing of estimated expenditures is considered reliably determinable, CMS Energy and Consumers record the liability at its net present value, using a discount rate equal to the interest rate on monetary assets that are essentially risk-free and have maturities comparable to that of the environmental liability. CMS Energy and Consumers expense legal fees as incurred; fees incurred but not yet billed are accrued based on estimates of work performed. |
| Debt Issuance Costs, Discounts, Premiums, and Refinancing Costs | Debt Issuance Costs, Discounts, Premiums, and Refinancing Costs: Upon the issuance of long-term debt, CMS Energy and Consumers defer issuance costs, discounts, and premiums and amortize those amounts over the terms of the associated debt. Debt issuance costs are presented as a direct deduction from the carrying amount of long-term debt on the balance sheet. Upon the refinancing of long-term debt, Consumers, as a regulated entity, defers any remaining unamortized issuance costs, discounts, and premiums associated with the refinanced debt and amortizes those amounts over the term of the newly issued debt. For the non‑regulated portions of CMS Energy’s business, any remaining unamortized issuance costs, discounts, and premiums associated with extinguished debt are charged to earnings. |
| Derivative Instruments | Derivative Instruments: In order to support ongoing operations, CMS Energy and Consumers enter into contracts for the future purchase and sale of various commodities, such as electricity, natural gas, and coal. These forward contracts are generally long-term in nature and result in physical delivery of the commodity at a contracted price. Most of these contracts are not subject to derivative accounting for one or more of the following reasons: • they do not have a notional amount (that is, a number of units specified in a derivative instrument, such as MWh of electricity or bcf of natural gas) • they qualify for the normal purchases and sales exception • they cannot be net settled due in part to the absence of an active market for the commodity Consumers also uses FTRs to manage price risk related to electricity transmission congestion. An FTR is a financial instrument that entitles its holder to receive compensation or requires its holder to remit payment for congestion-related transmission charges. Consumers accounts for FTRs as derivatives. Additionally, CMS Energy uses interest rate swaps to manage its interest rate risk on certain long-term debt and notes receivable transactions. CMS Energy and Consumers record derivative contracts that do not qualify for the normal purchases and sales exception at fair value on their consolidated balance sheets. At CMS Energy, if the derivative is accounted for as a cash flow hedge, unrealized gains and losses from changes in the fair value of the derivative are recognized in AOCI and subsequently recognized in earnings when the hedged transactions impact earnings. If the derivative is accounted for as a fair value hedge, changes in the fair value of the derivative and changes in the fair value of the hedged item due to the hedged risk are recognized in earnings. For the FTRs at Consumers, changes in fair value are deferred as regulatory assets or liabilities. For details regarding CMS Energy’s and Consumers’ derivative instruments recorded at fair value, see Note 6, Fair Value Measurements. |
| EPS | EPS: CMS Energy calculates basic and diluted EPS using the weighted-average number of shares of common stock and dilutive potential common stock outstanding during the period. Potential common stock, for purposes of determining diluted EPS, includes the effects of nonvested stock awards and forward equity sales. CMS Energy computes the effect on potential common stock using the treasury stock method. Diluted EPS excludes the impact of antidilutive securities, which are those securities resulting in an increase in EPS or a decrease in loss per share. For EPS computations, see Note 15, Earnings Per Share—CMS Energy. |
| Impairment of Long-Lived Assets | Impairment of Long-Lived Assets and Equity Method Investments: CMS Energy and Consumers perform tests of impairment if certain triggering events occur or if there has been a decline in value that may be other than temporary. CMS Energy and Consumers evaluate long-lived assets held in use for impairment by calculating the undiscounted future cash flows expected to result from the use of the asset and its eventual disposition. If the undiscounted future cash flows are less than the carrying amount, CMS Energy and Consumers recognize an impairment loss equal to the amount by which the carrying amount exceeds the fair value. CMS Energy and Consumers estimate the fair value of the asset using quoted market prices, market prices of similar assets, or discounted future cash flow analyses. |
| Impairment of Equity Method Investments | CMS Energy also assesses equity method investments for impairment whenever there has been a decline in value that is other than temporary. This assessment requires CMS Energy to determine the fair value of the equity method investment. CMS Energy determines fair value using valuation methodologies, including discounted cash flows, and assesses the ability of the investee to sustain an earnings capacity that justifies the carrying amount of the investment. CMS Energy records an impairment if the fair value is less than the carrying amount and the decline in value is considered to be other than temporary. |
| Investment Tax Credits | Investment Tax Credits: Consumers amortizes its investment tax credits over the life of the related property in accordance with regulatory treatment. CMS Energy’s non‑regulated businesses use the deferral method of accounting for investment tax credits. Under the deferral method, the book basis of the associated assets is reduced by the amount of the credit, resulting in lower depreciation expense over the life of the assets. Furthermore, the tax basis of the assets is reduced by 50 percent of the related credit, resulting in a net deferred tax asset. CMS Energy recognizes the tax benefit of this basis difference as a reduction to income tax expense in the year in which the plant reaches commercial operation. |
| Inventory - Gas and Coal | Inventory: CMS Energy and Consumers use the weighted-average cost method for valuing working gas, recoverable base gas in underground storage facilities, and materials and supplies inventory. CMS Energy and Consumers also use this method for valuing coal inventory, and they classify these amounts as generating plant fuel stock on their consolidated balance sheets. |
| Inventory - RECs and Emission Allowances | CMS Energy and Consumers account for RECs and emission allowances as inventory and use the weighted-average cost method to remove amounts from inventory. RECs and emission allowances are used to satisfy compliance obligations related to the generation of power. CMS Energy and Consumers classify these amounts within other assets on their consolidated balance sheets. |
| Inventory - Impairment | CMS Energy and Consumers evaluate inventory for impairment as required to ensure that its carrying value does not exceed the lower of cost or net realizable value. |
| MISO Transactions | MISO Transactions: MISO requires the submission of hourly day-ahead and real-time bids and offers for energy at locations across the MISO region. CMS Energy and Consumers account for MISO transactions on a net hourly basis in each of the real-time and day-ahead markets, netted across all MISO energy market locations. CMS Energy and Consumers record net hourly purchases in purchased and interchange power and net hourly sales in operating revenue on their consolidated statements of income. They record net billing adjustments upon receipt of settlement statements, record accruals for future net purchases and sales adjustments based on historical experience, and reconcile accruals to actual expenses and sales upon receipt of settlement statements. |
| Property Taxes | Property Taxes: Property taxes are based on the taxable value of Consumers’ real and personal property assessed by local taxing authorities. Consumers records property tax expense over the fiscal year of the taxing authority for which the taxes are levied. The deferred property tax balance represents the amount of Consumers’ accrued property tax that will be recognized over future governmental fiscal periods. |
| Renewable Energy Grant | Renewable Energy Grant: In 2013, Consumers received a renewable energy cash grant for Lake Winds ® Energy Park under Section 1603 of the American Recovery and Reinvestment Tax Act of 2009. Upon receipt of the grant, Consumers recorded a regulatory liability, which Consumers is amortizing over the life of Lake Winds ® Energy Park. Consumers presents the amortization as a reduction to maintenance and other operating expenses on its consolidated statements of income. Consumers recorded the deferred income taxes related to the grant as a reduction of the book basis of Lake Winds ® Energy Park. |
| New Accounting Standards | Implementation of New Accounting Standards ASU 2016‑13, Measurement of Credit Losses on Financial Instruments: This standard, which was effective on January 1, 2020 for CMS Energy and Consumers, provides new guidance for measuring and recognizing credit losses on financial instruments. The standard applies to financial assets that are not measured at fair value through net income as well as to certain off‑balance-sheet credit exposures. CMS Energy and Consumers were required to apply the standard using a modified retrospective approach, under which the initial impacts of the standard are recorded through a cumulative-effect adjustment to beginning retained earnings on the effective date. The standard required an increase to the allowance for loan losses at EnerBank. Prior to the standard, the allowance reflected expected credit losses over a 12‑month period, but the new guidance requires the allowance to reflect expected credit losses over the entire life of the loans. As a result, CMS Energy recorded a $65 million increase to its expected credit loss reserves on January 1, 2020, with the offsetting adjustment recorded to retained earnings, net of taxes of $14 million. The standard also requires an increase in the initial provision for loan losses recognized in net income for new loans originated in 2020 and beyond. The adoption of this standard resulted in a $21 million reduction to CMS Energy’s income before income taxes for the year ended December 31, 2020. For further information on EnerBank’s loans and the related allowance for loan losses see Note 8, Notes Receivable. At Consumers, the standard applies to the allowance for uncollectible accounts, but did not result in any significant changes to the allowance methodology and did not have a material impact on Consumers’ consolidated financial statements. ASU 2020-04, Facilitation of the Effects of Reference Rate Reform on Financial Reporting: This standard, which was effective as of March 12, 2020 for CMS Energy and Consumers, provides optional guidance intended to ease the potential burden in accounting for the expected discontinuation of LIBOR as a reference rate in the financial markets. The guidance can be applied to modifications made to certain contracts to replace LIBOR with a new reference rate. The guidance, if elected, will permit entities to treat such modifications as the continuation of the original contract, without any required accounting reassessments or remeasurements. The guidance will also facilitate the continuation of hedge accounting for derivatives that may have to be modified to incorporate a new rate. The guidance is effective through December 31, 2022. CMS Energy and Consumers presently have various contracts that reference LIBOR and they are assessing how this standard may be applied to specific contract modifications. |
| Allowance For Loan Losses Policy | Authorized contractors pay fees to EnerBank to provide borrowers with same-as-cash, zero interest, or reduced interest loans. Unearned income associated with the loan fees, which is recorded as a reduction to notes receivable on CMS Energy’s consolidated balance sheets, was $128 million at December 31, 2020 and $134 million at December 31, 2019. During 2020, EnerBank purchased portfolios of secured and unsecured consumer installment loans with a principal value of $90 million. During 2020, EnerBank completed sales of notes receivable with a principal value of $246 million and recorded gains of $6 million. EnerBank utilizes FICO scores as a key credit quality indicator when underwriting new loans and in assessing the credit exposures in its loan portfolio. The score is determined at the time of a borrower’s application and is generally not updated since the average duration of loans is about two years. At December 31, 2020, 86 percent of EnerBank’s loans had a FICO score rating between good and excellent. At December 31, 2020, 97 percent of EnerBank’s loan portfolio was originated within the past five years. The allowance for loan losses at December 31, 2020 reflects expected credit losses over the entire lifetime of the loan portfolio. EnerBank estimates the allowance by using the “weighted-average remaining maturity” methodology for their term loans, and the “probability of default and loss given default” methodology for their same-as-cash loans. These methodologies consider historical loan loss experience, prepayment expectations, and credit quality indicators. EnerBank considers current and projected economic conditions, and other reasonable and supportable forecast information to determine if adjustments to the allowance are necessary. The allowance is increased by the provision for loan losses and decreased by loan charge‑offs net of recoveries. Loan losses are charged against the allowance when the loss is confirmed, but no later than the point at which a loan becomes 120 days past due. |
| Property, Plant and Equipment, Capitalization | Capitalization: CMS Energy and Consumers record plant, property, and equipment at original cost when placed into service. The cost includes labor, material, applicable taxes, overhead such as pension and other benefits, and AFUDC, if applicable. Consumers’ plant, property, and equipment is generally recoverable through its general ratemaking process. |
| Plant Retirement and Abandonment Policy | With the exception of utility property for which the remaining book value has been securitized, mothballed utility property stays in rate base and continues to be depreciated at the same rate as before the mothball period. When utility property is retired or otherwise disposed of in the ordinary course of business, Consumers records the original cost to accumulated depreciation, along with associated cost of removal, net of salvage. CMS Energy and Consumers recognize gains or losses on the retirement or disposal of non‑regulated assets in income. Consumers records cost of removal collected from customers, but not spent, as a regulatory liability. |
| AFUDC | AFUDC: Consumers capitalizes AFUDC on regulated major construction projects, except pollution control facilities on its fossil-fuel-fired power plants. AFUDC represents the estimated cost of debt and authorized return-on-equity funds used to finance construction additions. Consumers records the offsetting credit as a reduction of interest for the amount representing the borrowed funds component and as other income for the equity funds component on the consolidated statements of income. When construction is completed and the property is placed in service, Consumers depreciates and recovers the capitalized AFUDC from customers over the life of the related asset. |
| Property, Plant and Equipment, Planned Major Maintenance Activities | CMS Energy and Consumers record property repairs and minor property replacement as maintenance expense. CMS Energy and Consumers record planned major maintenance activities as operating expense unless the cost represents the acquisition of additional long-lived assets or the replacement of an existing long-lived asset. |
| Asset Retirement Obligations Policy | CMS Energy and Consumers record the fair value of the cost to remove assets at the end of their useful lives, if there is a legal obligation to remove them. If a reasonable estimate of fair value cannot be made in the period in which the ARO is incurred, such as for assets with indeterminate lives, the liability is recognized when a reasonable estimate of fair value can be made. CMS Energy and Consumers have not recorded liabilities associated with the closure of certain gas wells that have an indeterminate life. CMS Energy and Consumers have not recorded liabilities for assets that have immaterial cumulative disposal costs, such as substation batteries. CMS Energy and Consumers calculate the fair value of ARO liabilities using an expected present-value technique that reflects assumptions about costs and inflation, and uses a credit-adjusted risk-free rate to discount the expected cash flows. CMS Energy’s ARO liabilities are primarily at Consumers. |
| Income Tax Policy | CMS Energy and its subsidiaries file a consolidated U.S. federal income tax return as well as a Michigan Corporate Income Tax return for the unitary business group and various other state unitary group combined income tax returns. Income taxes are allocated based on each company’s separate taxable income in accordance with the CMS Energy tax sharing agreement. |
| Revenue | Electric and Gas Utilities Consumers Utility Revenue: Consumers recognizes revenue primarily from the sale of electric and gas utility services at tariff-based rates regulated by the MPSC. Consumers’ customer base consists of a mix of residential, commercial, and diversified industrial customers. Consumers’ tariff-based sales performance obligations are described below. • Consumers has performance obligations for the service of standing ready to deliver electricity or natural gas to customers, and it satisfies these performance obligations over time. Consumers recognizes revenue at a fixed rate as it provides these services. These arrangements generally do not have fixed terms and remain in effect as long as the customer consumes the utility service. The rates are set by the MPSC through the rate-making process and represent the stand-alone selling price of Consumers’ service to stand ready to deliver. • Consumers has performance obligations for the service of delivering the commodity of electricity or natural gas to customers, and it satisfies these performance obligations upon delivery. Consumers recognizes revenue at a price per unit of electricity or natural gas delivered, based on the tariffs established by the MPSC. These arrangements generally do not have fixed terms and remain in effect as long as the customer consumes the utility service. The rates are set by the MPSC through the rate-making process and represent the stand-alone selling price of a bundled product comprising the commodity, electricity or natural gas, and the service of delivering such commodity. In some instances, Consumers has specific fixed-term contracts with large commercial and industrial customers to provide electricity or gas at certain tariff rates or to provide gas transportation services at contracted rates. The amount of electricity and gas to be delivered under these contracts and the associated future revenue to be received are generally dependent on the customers’ needs. Accordingly, Consumers recognizes revenues at the tariff or contracted rate as electricity or gas is delivered to the customer. Consumers also has other miscellaneous contracts with customers related to pole and other property rentals, appliance service plans, and utility contract work. Generally, these contracts are short term or evergreen in nature. Accounts Receivable and Unbilled Revenues: Accounts receivable comprise trade receivables and unbilled receivables. CMS Energy and Consumers record their accounts receivable at cost less an allowance for uncollectible accounts. The allowance is increased for uncollectible accounts expense and decreased for account write-offs net of recoveries. CMS Energy and Consumers establish the allowance based on historical losses, management’s assessment of existing economic conditions, customer payment trends, and reasonable and supported forecast information. CMS Energy and Consumers assess late payment fees on trade receivables based on contractual past-due terms established with customers. Accounts are written off when deemed uncollectible, which is generally when they become six months past due. CMS Energy and Consumers recorded uncollectible accounts expense of $33 million for the year ended December 31, 2020, and $29 million for the years ended December 31, 2019 and 2018. At December 31, 2020, Consumers had deferred $4 million of uncollectible accounts expense as a non-current regulatory asset. For additional information, see Note 3, Regulatory Matters. Consumers’ customers are billed monthly in cycles having billing dates that do not generally coincide with the end of a calendar month. This results in customers having received electricity or natural gas that they have not been billed for as of the month-end. Consumers estimates its unbilled revenues by applying an average billed rate to total unbilled deliveries for each customer class. Unbilled revenues, which are recorded as accounts receivable and accrued revenue on CMS Energy’s and Consumers’ consolidated balance sheets, were $437 million at December 31, 2020 and $426 million at December 31, 2019. Alternative ‑ Revenue Programs: Consumers accounts for its energy waste reduction incentive mechanism and financial compensation mechanism as alternative-revenue programs. Consumers recognizes revenue related to the energy waste reduction incentive as soon as energy savings exceed the annual targets established by the MPSC and recognizes revenue related to the financial compensation mechanism as payments are made on MPSC-approved PPAs. For additional information on these mechanisms, see Note 3, Regulatory Matters. Consumers does not reclassify revenue from its alternative-revenue program to revenue from contracts with customers at the time the amounts are collected from customers. |
| Cash and Cash Equivalents | Cash and Cash Equivalents: Cash and cash equivalents include short-term, highly liquid investments with original maturities of three months or less. |
| Restricted Cash and Cash Equivalents | Restricted Cash and Cash Equivalents: Restricted cash and cash equivalents are held primarily for the repayment of securitization bonds and funds held in escrow. Cash and cash equivalents may also be restricted to pay other contractual obligations such as leasing of coal railcars. These amounts are classified as current assets since they relate to payments that could or will occur within one year. |
| Software development | |
| Significant Accounting Policies [Line Items] | |
| Property, Plant and Equipment, Capitalization | Software: CMS Energy and Consumers capitalize the costs to purchase and develop internal-use computer software. These costs are expensed evenly over the estimated useful life of the internal-use computer software. If computer software is integral to computer hardware, then its cost is capitalized and depreciated with the hardware. |
| Variable Interest Entity, Primary Beneficiary | |
| Significant Accounting Policies [Line Items] | |
| Consolidation, Variable Interest Entity, Policy | Aviator Wind Equity Holdings and Aviator Wind represent VIEs. In accordance with the associated limited liability company operating agreement, the tax equity investor is guaranteed preferred returns from Aviator Wind. However, CMS Enterprises manages and controls the operating activities of Aviator Wind Equity Holdings and, ultimately, Aviator Wind. As a result, CMS Enterprises is the primary beneficiary of Aviator Wind Equity Holdings and Aviator Wind, as it has the power to direct the activities that most significantly impact the economic performance of the companies, as well as the obligation to absorb losses or the right to receive benefits from the companies. |
| Variable Interest Entity, Not Primary Beneficiary | |
| Significant Accounting Policies [Line Items] | |
| Consolidation, Variable Interest Entity, Policy | CMS Energy has variable interests in T.E.S. Filer City, Grayling, Genesee, and Craven. While CMS Energy owns 50 percent of each partnership, it is not the primary beneficiary of any of these partnerships because decision making is shared among unrelated parties, and no one party has the ability to direct the activities that most significantly impact the entities’ economic performance, such as operations and maintenance, plant dispatch, and fuel strategy. The partners must agree on all major decisions for each of the partnerships. |
| Consumers Energy Company | |
| Significant Accounting Policies [Line Items] | |
| Principles of Consolidation | Principles of Consolidation: CMS Energy and Consumers prepare their consolidated financial statements in conformity with GAAP. CMS Energy’s consolidated financial statements comprise CMS Energy, Consumers, CMS Enterprises, EnerBank, and all other entities in which CMS Energy has a controlling financial interest or is the primary beneficiary. Consumers’ consolidated financial statements comprise Consumers and all other entities in which it has a controlling financial interest or is the primary beneficiary. CMS Energy uses the equity method of accounting for investments in companies and partnerships that are not consolidated, where they have significant influence over operations and financial policies but are not the primary beneficiary. CMS Energy and Consumers eliminate intercompany transactions and balances. |
| Use of Estimates | Use of Estimates: CMS Energy and Consumers are required to make estimates using assumptions that may affect reported amounts and disclosures. Actual results could differ from those estimates. |
| Contingencies | Contingencies: CMS Energy and Consumers record estimated liabilities for contingencies on their consolidated financial statements when it is probable that a liability has been incurred and when the amount of loss can be reasonably estimated. For environmental remediation projects in which the timing of estimated expenditures is considered reliably determinable, CMS Energy and Consumers record the liability at its net present value, using a discount rate equal to the interest rate on monetary assets that are essentially risk-free and have maturities comparable to that of the environmental liability. CMS Energy and Consumers expense legal fees as incurred; fees incurred but not yet billed are accrued based on estimates of work performed. |
| Debt Issuance Costs, Discounts, Premiums, and Refinancing Costs | Debt Issuance Costs, Discounts, Premiums, and Refinancing Costs: Upon the issuance of long-term debt, CMS Energy and Consumers defer issuance costs, discounts, and premiums and amortize those amounts over the terms of the associated debt. Debt issuance costs are presented as a direct deduction from the carrying amount of long-term debt on the balance sheet. Upon the refinancing of long-term debt, Consumers, as a regulated entity, defers any remaining unamortized issuance costs, discounts, and premiums associated with the refinanced debt and amortizes those amounts over the term of the newly issued debt. For the non‑regulated portions of CMS Energy’s business, any remaining unamortized issuance costs, discounts, and premiums associated with extinguished debt are charged to earnings. |
| Derivative Instruments | Derivative Instruments: In order to support ongoing operations, CMS Energy and Consumers enter into contracts for the future purchase and sale of various commodities, such as electricity, natural gas, and coal. These forward contracts are generally long-term in nature and result in physical delivery of the commodity at a contracted price. Most of these contracts are not subject to derivative accounting for one or more of the following reasons: • they do not have a notional amount (that is, a number of units specified in a derivative instrument, such as MWh of electricity or bcf of natural gas) • they qualify for the normal purchases and sales exception • they cannot be net settled due in part to the absence of an active market for the commodity Consumers also uses FTRs to manage price risk related to electricity transmission congestion. An FTR is a financial instrument that entitles its holder to receive compensation or requires its holder to remit payment for congestion-related transmission charges. Consumers accounts for FTRs as derivatives. Additionally, CMS Energy uses interest rate swaps to manage its interest rate risk on certain long-term debt and notes receivable transactions. CMS Energy and Consumers record derivative contracts that do not qualify for the normal purchases and sales exception at fair value on their consolidated balance sheets. At CMS Energy, if the derivative is accounted for as a cash flow hedge, unrealized gains and losses from changes in the fair value of the derivative are recognized in AOCI and subsequently recognized in earnings when the hedged transactions impact earnings. If the derivative is accounted for as a fair value hedge, changes in the fair value of the derivative and changes in the fair value of the hedged item due to the hedged risk are recognized in earnings. For the FTRs at Consumers, changes in fair value are deferred as regulatory assets or liabilities. For details regarding CMS Energy’s and Consumers’ derivative instruments recorded at fair value, see Note 6, Fair Value Measurements. |
| Impairment of Long-Lived Assets | Impairment of Long-Lived Assets and Equity Method Investments: CMS Energy and Consumers perform tests of impairment if certain triggering events occur or if there has been a decline in value that may be other than temporary. CMS Energy and Consumers evaluate long-lived assets held in use for impairment by calculating the undiscounted future cash flows expected to result from the use of the asset and its eventual disposition. If the undiscounted future cash flows are less than the carrying amount, CMS Energy and Consumers recognize an impairment loss equal to the amount by which the carrying amount exceeds the fair value. CMS Energy and Consumers estimate the fair value of the asset using quoted market prices, market prices of similar assets, or discounted future cash flow analyses. |
| Investment Tax Credits | Investment Tax Credits: Consumers amortizes its investment tax credits over the life of the related property in accordance with regulatory treatment. CMS Energy’s non‑regulated businesses use the deferral method of accounting for investment tax credits. Under the deferral method, the book basis of the associated assets is reduced by the amount of the credit, resulting in lower depreciation expense over the life of the assets. Furthermore, the tax basis of the assets is reduced by 50 percent of the related credit, resulting in a net deferred tax asset. CMS Energy recognizes the tax benefit of this basis difference as a reduction to income tax expense in the year in which the plant reaches commercial operation. |
| Inventory - Gas and Coal | Inventory: CMS Energy and Consumers use the weighted-average cost method for valuing working gas, recoverable base gas in underground storage facilities, and materials and supplies inventory. CMS Energy and Consumers also use this method for valuing coal inventory, and they classify these amounts as generating plant fuel stock on their consolidated balance sheets. |
| Inventory - RECs and Emission Allowances | CMS Energy and Consumers account for RECs and emission allowances as inventory and use the weighted-average cost method to remove amounts from inventory. RECs and emission allowances are used to satisfy compliance obligations related to the generation of power. CMS Energy and Consumers classify these amounts within other assets on their consolidated balance sheets. |
| Inventory - Impairment | CMS Energy and Consumers evaluate inventory for impairment as required to ensure that its carrying value does not exceed the lower of cost or net realizable value. |
| MISO Transactions | MISO Transactions: MISO requires the submission of hourly day-ahead and real-time bids and offers for energy at locations across the MISO region. CMS Energy and Consumers account for MISO transactions on a net hourly basis in each of the real-time and day-ahead markets, netted across all MISO energy market locations. CMS Energy and Consumers record net hourly purchases in purchased and interchange power and net hourly sales in operating revenue on their consolidated statements of income. They record net billing adjustments upon receipt of settlement statements, record accruals for future net purchases and sales adjustments based on historical experience, and reconcile accruals to actual expenses and sales upon receipt of settlement statements. |
| Property Taxes | Property Taxes: Property taxes are based on the taxable value of Consumers’ real and personal property assessed by local taxing authorities. Consumers records property tax expense over the fiscal year of the taxing authority for which the taxes are levied. The deferred property tax balance represents the amount of Consumers’ accrued property tax that will be recognized over future governmental fiscal periods. |
| Renewable Energy Grant | Renewable Energy Grant: In 2013, Consumers received a renewable energy cash grant for Lake Winds ® Energy Park under Section 1603 of the American Recovery and Reinvestment Tax Act of 2009. Upon receipt of the grant, Consumers recorded a regulatory liability, which Consumers is amortizing over the life of Lake Winds ® Energy Park. Consumers presents the amortization as a reduction to maintenance and other operating expenses on its consolidated statements of income. Consumers recorded the deferred income taxes related to the grant as a reduction of the book basis of Lake Winds ® Energy Park. |
| New Accounting Standards | Implementation of New Accounting Standards ASU 2016‑13, Measurement of Credit Losses on Financial Instruments: This standard, which was effective on January 1, 2020 for CMS Energy and Consumers, provides new guidance for measuring and recognizing credit losses on financial instruments. The standard applies to financial assets that are not measured at fair value through net income as well as to certain off‑balance-sheet credit exposures. CMS Energy and Consumers were required to apply the standard using a modified retrospective approach, under which the initial impacts of the standard are recorded through a cumulative-effect adjustment to beginning retained earnings on the effective date. The standard required an increase to the allowance for loan losses at EnerBank. Prior to the standard, the allowance reflected expected credit losses over a 12‑month period, but the new guidance requires the allowance to reflect expected credit losses over the entire life of the loans. As a result, CMS Energy recorded a $65 million increase to its expected credit loss reserves on January 1, 2020, with the offsetting adjustment recorded to retained earnings, net of taxes of $14 million. The standard also requires an increase in the initial provision for loan losses recognized in net income for new loans originated in 2020 and beyond. The adoption of this standard resulted in a $21 million reduction to CMS Energy’s income before income taxes for the year ended December 31, 2020. For further information on EnerBank’s loans and the related allowance for loan losses see Note 8, Notes Receivable. At Consumers, the standard applies to the allowance for uncollectible accounts, but did not result in any significant changes to the allowance methodology and did not have a material impact on Consumers’ consolidated financial statements. ASU 2020-04, Facilitation of the Effects of Reference Rate Reform on Financial Reporting: This standard, which was effective as of March 12, 2020 for CMS Energy and Consumers, provides optional guidance intended to ease the potential burden in accounting for the expected discontinuation of LIBOR as a reference rate in the financial markets. The guidance can be applied to modifications made to certain contracts to replace LIBOR with a new reference rate. The guidance, if elected, will permit entities to treat such modifications as the continuation of the original contract, without any required accounting reassessments or remeasurements. The guidance will also facilitate the continuation of hedge accounting for derivatives that may have to be modified to incorporate a new rate. The guidance is effective through December 31, 2022. CMS Energy and Consumers presently have various contracts that reference LIBOR and they are assessing how this standard may be applied to specific contract modifications. |
| Property, Plant and Equipment, Capitalization | Capitalization: CMS Energy and Consumers record plant, property, and equipment at original cost when placed into service. The cost includes labor, material, applicable taxes, overhead such as pension and other benefits, and AFUDC, if applicable. Consumers’ plant, property, and equipment is generally recoverable through its general ratemaking process. |
| Plant Retirement and Abandonment Policy | With the exception of utility property for which the remaining book value has been securitized, mothballed utility property stays in rate base and continues to be depreciated at the same rate as before the mothball period. When utility property is retired or otherwise disposed of in the ordinary course of business, Consumers records the original cost to accumulated depreciation, along with associated cost of removal, net of salvage. CMS Energy and Consumers recognize gains or losses on the retirement or disposal of non‑regulated assets in income. Consumers records cost of removal collected from customers, but not spent, as a regulatory liability. |
| AFUDC | AFUDC: Consumers capitalizes AFUDC on regulated major construction projects, except pollution control facilities on its fossil-fuel-fired power plants. AFUDC represents the estimated cost of debt and authorized return-on-equity funds used to finance construction additions. Consumers records the offsetting credit as a reduction of interest for the amount representing the borrowed funds component and as other income for the equity funds component on the consolidated statements of income. When construction is completed and the property is placed in service, Consumers depreciates and recovers the capitalized AFUDC from customers over the life of the related asset. |
| Regulatory Depreciation and Amortization | Consumers depreciates utility property on an asset-group basis, in which it applies a single MPSC-approved depreciation rate to the gross investment in a particular class of property within the electric and gas segments. Consumers performs depreciation studies periodically to determine appropriate group lives. |
| Property, Plant and Equipment, Planned Major Maintenance Activities | CMS Energy and Consumers record property repairs and minor property replacement as maintenance expense. CMS Energy and Consumers record planned major maintenance activities as operating expense unless the cost represents the acquisition of additional long-lived assets or the replacement of an existing long-lived asset. |
| Asset Retirement Obligations Policy | CMS Energy and Consumers record the fair value of the cost to remove assets at the end of their useful lives, if there is a legal obligation to remove them. If a reasonable estimate of fair value cannot be made in the period in which the ARO is incurred, such as for assets with indeterminate lives, the liability is recognized when a reasonable estimate of fair value can be made. CMS Energy and Consumers have not recorded liabilities associated with the closure of certain gas wells that have an indeterminate life. CMS Energy and Consumers have not recorded liabilities for assets that have immaterial cumulative disposal costs, such as substation batteries. CMS Energy and Consumers calculate the fair value of ARO liabilities using an expected present-value technique that reflects assumptions about costs and inflation, and uses a credit-adjusted risk-free rate to discount the expected cash flows. CMS Energy’s ARO liabilities are primarily at Consumers. |
| Income Tax Policy | CMS Energy and its subsidiaries file a consolidated U.S. federal income tax return as well as a Michigan Corporate Income Tax return for the unitary business group and various other state unitary group combined income tax returns. Income taxes are allocated based on each company’s separate taxable income in accordance with the CMS Energy tax sharing agreement. |
| Revenue | Electric and Gas Utilities Consumers Utility Revenue: Consumers recognizes revenue primarily from the sale of electric and gas utility services at tariff-based rates regulated by the MPSC. Consumers’ customer base consists of a mix of residential, commercial, and diversified industrial customers. Consumers’ tariff-based sales performance obligations are described below. • Consumers has performance obligations for the service of standing ready to deliver electricity or natural gas to customers, and it satisfies these performance obligations over time. Consumers recognizes revenue at a fixed rate as it provides these services. These arrangements generally do not have fixed terms and remain in effect as long as the customer consumes the utility service. The rates are set by the MPSC through the rate-making process and represent the stand-alone selling price of Consumers’ service to stand ready to deliver. • Consumers has performance obligations for the service of delivering the commodity of electricity or natural gas to customers, and it satisfies these performance obligations upon delivery. Consumers recognizes revenue at a price per unit of electricity or natural gas delivered, based on the tariffs established by the MPSC. These arrangements generally do not have fixed terms and remain in effect as long as the customer consumes the utility service. The rates are set by the MPSC through the rate-making process and represent the stand-alone selling price of a bundled product comprising the commodity, electricity or natural gas, and the service of delivering such commodity. In some instances, Consumers has specific fixed-term contracts with large commercial and industrial customers to provide electricity or gas at certain tariff rates or to provide gas transportation services at contracted rates. The amount of electricity and gas to be delivered under these contracts and the associated future revenue to be received are generally dependent on the customers’ needs. Accordingly, Consumers recognizes revenues at the tariff or contracted rate as electricity or gas is delivered to the customer. Consumers also has other miscellaneous contracts with customers related to pole and other property rentals, appliance service plans, and utility contract work. Generally, these contracts are short term or evergreen in nature. Accounts Receivable and Unbilled Revenues: Accounts receivable comprise trade receivables and unbilled receivables. CMS Energy and Consumers record their accounts receivable at cost less an allowance for uncollectible accounts. The allowance is increased for uncollectible accounts expense and decreased for account write-offs net of recoveries. CMS Energy and Consumers establish the allowance based on historical losses, management’s assessment of existing economic conditions, customer payment trends, and reasonable and supported forecast information. CMS Energy and Consumers assess late payment fees on trade receivables based on contractual past-due terms established with customers. Accounts are written off when deemed uncollectible, which is generally when they become six months past due. CMS Energy and Consumers recorded uncollectible accounts expense of $33 million for the year ended December 31, 2020, and $29 million for the years ended December 31, 2019 and 2018. At December 31, 2020, Consumers had deferred $4 million of uncollectible accounts expense as a non-current regulatory asset. For additional information, see Note 3, Regulatory Matters. Consumers’ customers are billed monthly in cycles having billing dates that do not generally coincide with the end of a calendar month. This results in customers having received electricity or natural gas that they have not been billed for as of the month-end. Consumers estimates its unbilled revenues by applying an average billed rate to total unbilled deliveries for each customer class. Unbilled revenues, which are recorded as accounts receivable and accrued revenue on CMS Energy’s and Consumers’ consolidated balance sheets, were $437 million at December 31, 2020 and $426 million at December 31, 2019. Alternative ‑ Revenue Programs: Consumers accounts for its energy waste reduction incentive mechanism and financial compensation mechanism as alternative-revenue programs. Consumers recognizes revenue related to the energy waste reduction incentive as soon as energy savings exceed the annual targets established by the MPSC and recognizes revenue related to the financial compensation mechanism as payments are made on MPSC-approved PPAs. For additional information on these mechanisms, see Note 3, Regulatory Matters. Consumers does not reclassify revenue from its alternative-revenue program to revenue from contracts with customers at the time the amounts are collected from customers. |
| Cash and Cash Equivalents | Cash and Cash Equivalents: Cash and cash equivalents include short-term, highly liquid investments with original maturities of three months or less. |
| Restricted Cash and Cash Equivalents | Restricted Cash and Cash Equivalents: Restricted cash and cash equivalents are held primarily for the repayment of securitization bonds and funds held in escrow. Cash and cash equivalents may also be restricted to pay other contractual obligations such as leasing of coal railcars. These amounts are classified as current assets since they relate to payments that could or will occur within one year. |
| Consumers Energy Company | Software development | |
| Significant Accounting Policies [Line Items] | |
| Property, Plant and Equipment, Capitalization | Software: CMS Energy and Consumers capitalize the costs to purchase and develop internal-use computer software. These costs are expensed evenly over the estimated useful life of the internal-use computer software. If computer software is integral to computer hardware, then its cost is capitalized and depreciated with the hardware. |
