Income Taxes (Loss and Credit Carryforwards) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Total tax attributes	$ 733
Consumers Energy Company [Member]
Total tax attributes	61
Internal Revenue Service (IRS) [Member]
Operating loss carryforward, Gross Amount	1,194
Federal net operating loss carryforward, Tax Attribute	418
Internal Revenue Service (IRS) [Member] | Consumers Energy Company [Member]
Operating loss carryforward, Gross Amount	163
Federal net operating loss carryforward, Tax Attribute	56
Local Jurisdiction [Member]
Operating loss carryforward, Gross Amount	433
Local net operating loss carryforwards, Tax Attribute	4
Valuation Allowance - Loss carryforward	1
State Jurisdiction [Member]
Capital loss carryforwards, Gross Amount	18
State capital loss carryforward, Tax Attribute	1
Valuation Allowance - Loss carryforward	1
State Jurisdiction [Member] | Consumers Energy Company [Member]
Capital loss carryforwards, Gross Amount	10
State capital loss carryforward, Tax Attribute	1
Valuation Allowance - Loss carryforward	1
Alternative Minimum Tax [Member]
Tax credits, Gross Amount	270
Alternative minimum tax credits, Tax Attribute	270
Alternative Minimum Tax [Member] | Consumers Energy Company [Member]
Tax credits, Gross Amount	2
Alternative minimum tax credits, Tax Attribute	2
Charitable Contribution Carryover [Member]
Charitable contribution carryforwards	6
Charitable contribution carryover, Tax Attribute	2
Charitable Contribution Carryover [Member] | Consumers Energy Company [Member]
Charitable contribution carryforwards	6
Charitable contribution carryover, Tax Attribute	2
General Business Tax Credit Carryforward [Member]
Tax credits, Gross Amount	38
General business credits, Tax Attribute	38
Valuation Allowance - General business credits	$ 1