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Retirement Benefits (Schedule of Net Periodic Benefit Cost Not yet Recognized) (Details) (USD $) In Millions, unless otherwise specified | Dec. 31, 2011 | Dec. 31, 2010
--- | --- | ---
Pension and SERP [Member] |  |
Pension and Other Postretirement Benefit Plans, Regulatory Assets, Net (Gains) Losses, before Tax | $ 1,014 | $ 914
Pension and Other Postretirement Benefit Plans, Regulatory Assets, Net Prior Service Cost (Credit), before Tax | 17 | 23
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net (Gains) Losses, before Tax | 81 | 72
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Prior Service Cost (Credit), before Tax | 2 | 2
Total amounts not yet recognized as component of net periodic benefit cost | 1,114 | 1,011
Pension and SERP [Member] | Consumers Energy Company [Member] |  |
Pension and Other Postretirement Benefit Plans, Regulatory Assets, Net (Gains) Losses, before Tax | 1,014 | 914
Pension and Other Postretirement Benefit Plans, Regulatory Assets, Net Prior Service Cost (Credit), before Tax | 17 | 23
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net (Gains) Losses, before Tax | 27 | 22
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Prior Service Cost (Credit), before Tax |  | 1
Total amounts not yet recognized as component of net periodic benefit cost | 1,058 | 960
Other Postretirement Benefit Plans, Defined Benefit [Member] |  |
Pension and Other Postretirement Benefit Plans, Regulatory Assets, Net (Gains) Losses, before Tax | 766 | 579
Pension and Other Postretirement Benefit Plans, Regulatory Assets, Net Prior Service Cost (Credit), before Tax | (132) | (152)
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net (Gains) Losses, before Tax | (5) | (9)
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Net Prior Service Cost (Credit), before Tax | (3) | (4)
Total amounts not yet recognized as component of net periodic benefit cost | 626 | 414
Other Postretirement Benefit Plans, Defined Benefit [Member] | Consumers Energy Company [Member] |  |
Pension and Other Postretirement Benefit Plans, Regulatory Assets, Net (Gains) Losses, before Tax | 766 | 579
Pension and Other Postretirement Benefit Plans, Regulatory Assets, Net Prior Service Cost (Credit), before Tax | (132) | (152)
Total amounts not yet recognized as component of net periodic benefit cost | $ 634 | $ 427

X
- Definition The pretax net amount of gains and losses that are not yet recognized as a component of net periodic benefit cost, and that are recognized as increases or decreases in regulatory assets as they arise. Gains and losses are due to changes in the value of either the benefit obligation or the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption, or the consequence of a decision to temporarily deviate from the substantive plan. + References No definition available. + Details
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X
- Definition Amount related to the pretax cost of benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation, which has not yet been recognized as components of net periodic benefit cost. + References No definition available. + Details
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X
- Definition Total amount of regulatory assets and AOCI that have not been recognized as a component of net periodic cost. + References No definition available. + Details
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X
- Definition The pretax net amount of gains and losses that are not yet recognized as a component of net periodic benefit cost, and that are recognized as increases or decreases in other comprehensive income as they arise. Gains and losses are due to changes in the value of either the benefit obligation or the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption, or the consequence of a decision to temporarily deviate from the substantive plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 132R -Paragraph 5 -Subparagraph i -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 Statement of Financial Accounting Standard (FAS) -Number 158 -Paragraph 7 -Subparagraph c -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 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e1928-114920 + Details
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X
- Definition Amount related to the pretax cost of benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation, which has not yet been recognized as components of net periodic benefit cost. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 87 -Paragraph 264 -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 (j) -URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 132R -Paragraph 5 -Subparagraph i -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 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Prior Service Cost -URI http://asc.fasb.org/extlink&oid=6521920 -Topic 715 -SubTopic 60 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 158 -Paragraph 7 -Subparagraph c -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 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 106 -Paragraph 518 -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 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Prior Service Cost -URI http://asc.fasb.org/extlink&oid=6521884 -Topic 715 -SubTopic 30 + Details
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