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Retirement Benefits (Schedule Of Retirement Benefit Plan Assets (Liabilities)) (Details) - USD ($) $ in Millions | Dec. 31, 2016 | Dec. 31, 2015
--- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |
Non-current liabilities | $ 789 | $ 591
Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Non-current liabilities | 730 | 529
DB Pension Plan [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Non-current liabilities | 461 | 390
DB Pension Plan [Member] | Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Non-current liabilities | 441 | 368
DB SERP [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Current liabilities | 8 | 8
Non-current liabilities | 143 | 142
DB SERP [Member] | Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Current liabilities | 5 | 5
Non-current liabilities | 104 | 101
OPEB [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Non-current liabilities | 144 | 19
OPEB [Member] | Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Non-current liabilities | $ 181 | $ 55

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- Definition For a classified balance sheet, the amount recognized in balance sheet as a current liability associated with an underfunded defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Current Liabilities -URI http://asc.fasb.org/extlink&oid=6509677 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=64852052&loc=d3e1703-114919 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 + Details
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- Definition This represents the noncurrent liability for underfunded plans recognized in the balance sheet that is associated with the defined benefit pension plans and other postretirement defined benefit plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e2417-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=64852052&loc=d3e1703-114919 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.24) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e2410-114920 + Details
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