Significant Accounting Policies (Policy)	3 Months Ended
Mar. 31, 2021
Significant Accounting Policies [Line Items]
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 $122 million at March 31, 2021 and $128 million at December 31, 2020. During the three months ended March 31, 2021, EnerBank purchased portfolios of secured and unsecured consumer installment loans with a principal value of $33 million. During the three months ended March 31, 2021, EnerBank completed sales of notes receivable with a principal value of $279 million and recorded gains of $10 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 March 31, 2021, 86 percent of EnerBank’s loans had a FICO score rating between good and excellent. At March 31, 2021, 96 percent of EnerBank’s loan portfolio was originated within the past five years. The allowance for loan losses at March 31, 2021 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.
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.
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]
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.

Significant Accounting Policies (Policy)

3 Months Ended

Mar. 31, 2021

Significant Accounting Policies [Line Items]

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 $122 million at March 31, 2021 and $128 million at December 31, 2020.

During the three months ended March 31, 2021, EnerBank purchased portfolios of secured and unsecured consumer installment loans with a principal value of $33 million. During the three months ended March 31, 2021, EnerBank completed sales of notes receivable with a principal value of $279 million and recorded gains of $10 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 March 31, 2021, 86 percent of EnerBank’s loans had a FICO score rating between good and excellent. At March 31, 2021, 96 percent of EnerBank’s loan portfolio was originated within the past five years.

The allowance for loan losses at March 31, 2021 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.

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.

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]

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