Stock-Based Compensation (Narrative) (Details) $ in Millions	12 Months Ended
Dec. 31, 2015 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deferred Compensation Arrangements Plan Term	10 years
Number of shares authorized	6,500,000
Maximum shares issuable per employee	500,000
Shares available for grant	5,611,442
Tax benefits recognized in equity \| $	$ 1
Unrealized Adjustments to Additional Paid in Capital, Income Tax Benefit from Share-based Compensation \| $	$ 33
Consumers Energy Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deferred Compensation Arrangements Plan Term	10 years
Number of shares authorized	6,500,000
Maximum shares issuable per employee	500,000
Shares available for grant	5,611,442
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percent of Initial Grant Issued on Vesting Date	0.00%
Minimum [Member] \| Consumers Energy Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percent of Initial Grant Issued on Vesting Date	0.00%
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percent of Initial Grant Issued on Vesting Date	200.00%
Maximum [Member] \| Consumers Energy Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percent of Initial Grant Issued on Vesting Date	200.00%
Performance-Based Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service period	38 months
Vesting period	3 years
Performance-Based Restricted Stock [Member] \| Consumers Energy Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service period	38 months
Vesting period	3 years
Performance-Based Restricted Stock [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service period	36 months
Performance-Based Restricted Stock [Member] \| Minimum [Member] \| Consumers Energy Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service period	36 months
Market-Based Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service period	3 years
Market-Based Restricted Stock [Member] \| Consumers Energy Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service period	3 years
Time-Lapsed Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Time-Lapsed Restricted Stock [Member] \| Consumers Energy Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	3 years
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service period	1 year
Shares vested	0
Shares forfeited	0

Deferred Compensation Arrangements Plan Term

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

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- Definition

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

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- Definition

Unrealized tax benefit associated with any equity-based compensation plan other than an employee stock ownership plan (ESOP). The tax benefit cannot be recognized due to the use of tax loss carryforwards.

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Amount of increase in additional paid in capital (APIC) resulting from a tax benefit associated with share-based compensation plan other than an employee stock ownership plan (ESOP). Includes, but is not limited to, excess tax benefit.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 740
-Section 45
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-Publisher FASB
-Name Accounting Standards Codification
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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 which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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-Publisher FASB
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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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