Significant Accounting Policies (Policy)	9 Months Ended
	Sep. 30, 2021
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.
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.