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Financial Instruments (Summary Of Sales Activity For Investment Securities) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Financial Instruments [Line Items] |  |  |
Proceeds from DB SERP investments | $ 146 | $ 0 | $ 0
Consumers Energy Company |  |  |
Financial Instruments [Line Items] |  |  |
Proceeds from DB SERP investments | 106 | 0 | 0
DB SERP |  |  |
Financial Instruments [Line Items] |  |  |
Proceeds from DB SERP investments | 142 | 145 | 6
DB SERP | Consumers Energy Company |  |  |
Financial Instruments [Line Items] |  |  |
Proceeds from DB SERP investments | $ 103 | $ 105 | $ 4

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- Definition Financial Instruments [Line Items] + References No definition available. + Details
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- Definition Amount of cash inflow from sale of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26853-111562 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3151-108585 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 12 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3179-108585 + Details
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