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Retirement Benefits (Schedule Of Plan Contributions) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement benefits contributions | $ 108 | $ 262 | $ 32
Consumers Energy Company [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement benefits contributions | 98 | 243 | 29
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
DB Pension Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement benefits contributions | 100 | 225 |
DB Pension Plan [Member] | Consumers Energy Company [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Postretirement benefits contributions | $ 93 | $ 209 |
Equity Securities [Member] | Postretirement Health Trusts [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 50.00% |  |
Equity Securities [Member] | Postretirement Life Trusts [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 42.00% |  |
Equity Securities [Member] | DB Pension Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 53.00% |  |
Fixed Income Funds [Member] | Postretirement Health Trusts [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 30.00% |  |
Fixed Income Funds [Member] | Postretirement Life Trusts [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 28.00% |  |
Fixed Income Funds [Member] | DB Pension Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 32.00% |  |
Alternative Strategy Investments [Member] | Postretirement Health Trusts [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 20.00% |  |
Alternative Strategy Investments [Member] | Postretirement Life Trusts [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 30.00% |  |
Alternative Strategy Investments [Member] | DB Pension Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Defined Benefit Plan, Target Plan Asset Allocations | 15.00% |  |

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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=65897934&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=65897934&loc=d3e1928-114920 + 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=66902209&loc=d3e3536-108585 + Details
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