Contingencies and Commitments (Schedule of Remediation and Other Response Activity Costs by Year) (Details) $ in Millions	Sep. 30, 2025 USD ($)
Consumers Energy Company \| MGP sites
Site Contingency [Line Items]
2025	$ 0
2026	3
2027	8
2028	25
2029	11
2030	3
Bay Harbor
Site Contingency [Line Items]
2025	1
2026	4
2027	4
2028	4
2029	4
2030	$ 4

Undiscounted amount of accrual for environmental loss contingency to be paid in fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Undiscounted amount of accrual for environmental loss contingency to be paid in fourth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Undiscounted amount of accrual for environmental loss contingency to be paid in remainder of current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Undiscounted amount of accrual for environmental loss contingency to be paid in second fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Undiscounted amount of accrual for environmental loss contingency to be paid in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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