Stock-Based Compensation (Narrative) (Details) $ in Millions	12 Months Ended
Dec. 31, 2019 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deferred compensation arrangements plan term	10 years
Number of shares authorized (in shares)	6,500,000
Maximum shares issuable per employee (in shares)	500,000
Shares available for grant (in shares)	3,258,000
Consumers Energy Company
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deferred compensation arrangements plan term	10 years
Number of shares authorized (in shares)	6,500,000.0
Maximum shares issuable per employee (in shares)	500,000
Shares available for grant (in shares)	3,714,544
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percent of initial grant issued on vesting date	0.00%
Minimum \| Consumers Energy Company
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percent of initial grant issued on vesting date	0.00%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percent of initial grant issued on vesting date	200.00%
Maximum \| Consumers Energy Company
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percent of initial grant issued on vesting date	200.00%
Performance-based awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service period	38 months
Vesting period	3 years
Performance-based awards \| Consumers Energy Company
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service period	38 months
Vesting period	3 years
Performance-based awards \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service period	36 months
Performance-based awards \| Minimum \| Consumers Energy Company
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service period	36 months
Market-based awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service period	3 years
Vesting period	3 years
Market-based awards \| Consumers Energy Company
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service period	3 years
Vesting period	3 years
Time-lapse awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service period	3 years
Time-lapse awards \| Consumers Energy Company
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service period	3 years
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service period	1 year
Shares forfeited (in shares)	0
Restricted stock units \| Consumers Energy Company
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service period	1 year
Shares forfeited (in shares)	0
Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares forfeited (in shares)	46,949
Unrecognized compensation cost \| $	$ 21.7
Unrecognized compensation cost recognition period	2 years
Restricted stock \| Consumers Energy Company
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares forfeited (in shares)	40,139
Unrecognized compensation cost \| $	$ 20.8
Unrecognized compensation cost recognition period	2 years

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Percentage of initial grant of equity-based compensation awards earned depending on the outcome of the market condition or performance condition.

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The highest quantity of shares an employee can be awarded under the plan per period.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Amount of cost to be recognized for nonvested award under share-based payment arrangement. Excludes share and unit options.

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Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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Number of shares authorized for issuance under share-based payment arrangement.

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