New Accounting Standards (Policies)	9 Months Ended
New Accounting Standards (Policies)	Sep. 30, 2020
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
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 $15 million reduction to CMS Energy’s income before income taxes for the nine months ended September 30, 2020. For further information on EnerBank’s loans and the related allowance for loan losses, see Note 7, 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	The allowance for loan losses at September 30, 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.
Consumers Energy Company
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
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 $15 million reduction to CMS Energy’s income before income taxes for the nine months ended September 30, 2020. For further information on EnerBank’s loans and the related allowance for loan losses, see Note 7, 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.