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Retirement Benefits (Schedule Of Plan Contributions) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement benefits contributions | $ 262 | $ 32 | $ 229
Consumers Energy Company [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement benefits contributions | 243 | 29 | $ 222
OPEB [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement benefits contributions | 29 | 25 |
OPEB [Member] | Consumers Energy Company [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement benefits contributions | 29 | 25 |
Pension Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement benefits contributions | 225 |  |
Pension Plan [Member] | Consumers Energy Company [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement benefits contributions | 209 |  |
VEBA Trust [Member] | OPEB [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement benefits contributions | 29 | 16 |
VEBA Trust [Member] | OPEB [Member] | Consumers Energy Company [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement benefits contributions | $ 29 | 16 |
401 (h) Component [Member] | OPEB [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement benefits contributions |  | 9 |
401 (h) Component [Member] | OPEB [Member] | Consumers Energy Company [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement benefits contributions |  | $ 9 |
Equity Securities [Member] | OPEB [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 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% |  |
Equity Securities [Member] | Pension Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 50.00% |  |
Equity Securities [Member] | Pension Plan [Member] | Consumers Energy Company [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 50.00% |  |
Fixed Income Funds [Member] | OPEB [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 30.00% |  |
Fixed Income Funds [Member] | OPEB [Member] | Consumers Energy Company [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 30.00% |  |
Fixed Income Funds [Member] | Pension Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 30.00% |  |
Fixed Income Funds [Member] | Pension Plan [Member] | Consumers Energy Company [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 30.00% |  |
Alternative Strategy Investments [Member] | OPEB [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 20.00% |  |
Alternative Strategy Investments [Member] | OPEB [Member] | Consumers Energy Company [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 20.00% |  |
Alternative Strategy Investments [Member] | Pension Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 20.00% |  |
Alternative Strategy Investments [Member] | Pension Plan [Member] | Consumers Energy Company [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 20.00% |  |

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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 5 -Subparagraph (c)(i) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e2446-114920 Reference 2: 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=58740216&loc=d3e1928-114920 + Details
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