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Retirement Benefits (Schedule Of Plan Contributions) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Postretirement benefits contributions | $ 229 |  | $ 72 |  | $ 323
Consumers Energy Company [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Postretirement benefits contributions | 222 |  | 68 |  | 315
OPEB [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Postretirement benefits contributions | 72 | [1] | 65 | [1] |
Estimated future employer contributions | 75 |  |  |  |
OPEB [Member] | Consumers Energy Company [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Postretirement benefits contributions | 71 | [1] | 64 | [1] |
Estimated future employer contributions | 74 |  |  |  |
Pension [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Postretirement benefits contributions | 150 | [2] |  |  |
Pension [Member] | Consumers Energy Company [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Postretirement benefits contributions | 147 | [2] |  |  |
VEBA Trust [Member] | OPEB [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Postretirement benefits contributions | 55 | [1] | 45 | [1] |
VEBA Trust [Member] | OPEB [Member] | Consumers Energy Company [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Postretirement benefits contributions | 55 | [1] | 45 | [1] |
401 (h) Component [Member] | OPEB [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Postretirement benefits contributions | 17 | [1] | 20 | [1] |
401 (h) Component [Member] | OPEB [Member] | Consumers Energy Company [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Postretirement benefits contributions | $ 16 | [1] | $ 19 | [1] |
Equity Securities [Member] | OPEB [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 50.00% |  | 50.00% |  |
Equity Securities [Member] | OPEB [Member] | Consumers Energy Company [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 50.00% |  | 50.00% |  |
Equity Securities [Member] | Pension [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 50.00% |  | 50.00% |  | 50.00%
Equity Securities [Member] | Pension [Member] | Consumers Energy Company [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 50.00% |  | 50.00% |  | 50.00%
Fixed Income Funds [Member] | OPEB [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 20.00% |  | 20.00% |  |
Fixed Income Funds [Member] | OPEB [Member] | Consumers Energy Company [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 20.00% |  | 20.00% |  |
Fixed Income Funds [Member] | Pension [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 30.00% |  | 30.00% |  | 30.00%
Fixed Income Funds [Member] | Pension [Member] | Consumers Energy Company [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 30.00% |  | 30.00% |  | 30.00%
Alternative Strategy Investments [Member] | OPEB [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 30.00% |  | 30.00% |  |
Alternative Strategy Investments [Member] | OPEB [Member] | Consumers Energy Company [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 30.00% |  | 30.00% |  |
Alternative Strategy Investments [Member] | Pension [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 20.00% |  | 20.00% |  | 20.00%
Alternative Strategy Investments [Member] | Pension [Member] | Consumers Energy Company [Member] |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 20.00% |  | 20.00% |  | 20.00%
[1] | CMS Energy, including Consumers, plans to contribute $75 million to the OPEB Plan in 2014, of which Consumers plans to contribute $74 million.
[2] | CMS Energy, including Consumers, does not presently plan to contribute to the Pension Plan in 2014.

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- Definition Amount of employer's best estimate of contributions expected to be paid to the plan during the next fiscal year beginning after the date of the latest statement of financial position. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920 + Details
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- Definition Target allocation of investments of this type to total plan assets presented on a weighted average basis. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(i) -URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (c)(i) -URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e2446-114920 + Details
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- Definition The amount of cash or cash equivalents contributed during the reporting period by the entity to fund its pension plans and its non-pension postretirement benefit plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 25 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3536-108585 + Details
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