Retirement Benefits (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Concentration Risk, Percentage	42.00%
Consumers Energy Company [Member]
Concentration Risk, Percentage	44.00%
401 (k) Plan [Member]
Employer match of eligible contributions	60.00%
Employer match of eligible wages	6.00%
Savings Plan, Cost Recognized	$ 16	$ 16	$ 16
401 (k) Plan [Member] \| Consumers Energy Company [Member]
Employer match of eligible contributions	60.00%
Employer match of eligible wages	6.00%
Savings Plan, Cost Recognized	16	15	15
EISP [Member]
EISP expense less than million	1	1	1
Nonqualified separation plan, ABO	5	5
EISP [Member] \| Consumers Energy Company [Member]
EISP expense less than million	1	1	1
Nonqualified separation plan, ABO	1	1
Other Postretirement Benefit Plans, Defined Benefit [Member]
Retirement age requirement	55
Retirement years of service	10
Retirement years of service with disability	15
Defined Benefit Plan, Health Care Cost Trend Rate Assumed for Next Fiscal Year	7.50%	8.00%
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate	5.00%
Other Postretirement Benefit Plans, Defined Benefit [Member] \| Consumers Energy Company [Member]
Retirement age requirement	55
Retirement years of service	10
Retirement years of service with disability	15
Defined Benefit Plan, Health Care Cost Trend Rate Assumed for Next Fiscal Year	7.50%	8.00%
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate	5.00%
Defined Company Contribution Plan [Member]
Defined Contribution Plan, Cost Recognized (less than million for DC SERP)	7	5	4
Defined Company Contribution Plan [Member] \| Consumers Energy Company [Member]
Defined Contribution Plan, Cost Recognized (less than million for DC SERP)	7	5	4
Defined Company Contribution Plan [Member] \| Contributions After September 1, 2005 [Member]
Plan Contribution Percentage	5.00%
Defined Company Contribution Plan [Member] \| Contributions After September 1, 2005 [Member] \| Consumers Energy Company [Member]
Plan Contribution Percentage	5.00%
Defined Company Contribution Plan [Member] \| Contributions After January 1, 2011 [Member]
Plan Contribution Percentage	6.00%
Defined Company Contribution Plan [Member] \| Contributions After January 1, 2011 [Member] \| Consumers Energy Company [Member]
Plan Contribution Percentage	6.00%
Supplemental Employee Retirement Plan Defined Contribution [Member]
DC SERP Trust assets less than million	1	1
Defined Contribution Plan, Cost Recognized (less than million for DC SERP)	1	1	1
Supplemental Employee Retirement Plan Defined Contribution [Member] \| Consumers Energy Company [Member]
DC SERP Trust assets less than million	1	1
Defined Contribution Plan, Cost Recognized (less than million for DC SERP)	$ 1	$ 1	$ 1

Total trust assets in the DC SERP Trust fund.

No definition available.

Name:	cms_DcSerpTrustAssets
Namespace Prefix:	cms_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Expense for a nonqualified plan to provide flexibility in serparation of employment by officers, a selected group of management or other highly compenssated employees.

+ References

No definition available.

+ Details

Name:	cms_EispExpense
Namespace Prefix:	cms_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The employer match equals 60 percent of eligible contributions up to the first six percent of an employee's wages.

+ References

No definition available.

+ Details

Name:	cms_EmployerMatchOfEligibleContributions
Namespace Prefix:	cms_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The employer match equals 60 percent of eligible contributions up to the first six percent of an employee's wages.

+ References

No definition available.

+ Details

Name:	cms_EmployerMatchOfEligibleWages
Namespace Prefix:	cms_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Nonqualified separation plan accumulated benefit obligation.

+ References

No definition available.

+ Details

Name:	cms_NonqualifiedSeparationPlanAbo
Namespace Prefix:	cms_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Percentage of base pay contributed by the Company to the plan for employees.

+ References

No definition available.

+ Details

Name:	cms_PlanContributionPercentage
Namespace Prefix:	cms_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Participants in the plan include all regular full-time employees covered by the employee health care plan on the day before retirement at age 55 or older with at least ten full years of applicable continuous service. Regular full-time employees who qualify for Pension Plan disability retirement and have 15 years of applicable continuous service may also participate in the plan.

+ References

No definition available.

+ Details

Name:	cms_RetirementAgeRequirement
Namespace Prefix:	cms_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

+ References

No definition available.

+ Details

Name:	cms_RetirementYearsOfService
Namespace Prefix:	cms_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

+ References

No definition available.

+ Details

Name:	cms_RetirementYearsOfServiceWithDisability
Namespace Prefix:	cms_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of the cost recognized during the period for a savings plan.

+ References

No definition available.

+ Details

Name:	cms_SavingsPlanCostRecognized
Namespace Prefix:	cms_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6404-108592

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 21

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6947722&loc=d3e13537-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=6947722&loc=d3e13531-108611

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 18

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6351-108592

+ Details

Name:	us-gaap_ConcentrationRiskPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The assumed health care cost trend rate for the next year used to measure the expected cost of benefits covered by the plan (gross eligible charges). This is based upon the annual rate of change in the cost of health care benefits currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph l

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Health Care Cost Trend Rate

-URI http://asc.fasb.org/extlink&oid=6514820

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (l)

-URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e1928-114920

+ Details

Name:	us-gaap_DefinedBenefitPlanHealthCareCostTrendRateAssumedForNextFiscalYear
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The ultimate trend rate for health care costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph l

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (l)

-URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e1928-114920

+ Details

Name:	us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of the cost recognized during the period for defined contribution plans.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 11

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 70

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6414718&loc=d3e28014-114942

+ Details

Name:	us-gaap_DefinedContributionPlanCostRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration