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Revenue (Components of Operating Revenue) (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue recognized from contracts with customers |  |  |  |  |  |  |  |  | $ 6,502 |  |
Leasing income |  |  |  |  |  |  |  |  | 160 |  |
Financing income |  |  |  |  |  |  |  |  | 172 |  |
Consumers alternative revenue programs |  |  |  |  |  |  |  |  | 39 |  |
Total operating revenue | $ 1,829 | $ 1,599 | $ 1,492 | $ 1,953 | $ 1,778 | $ 1,527 | $ 1,449 | $ 1,829 | 6,873 | $ 6,583 | $ 6,399
Other reconciling items |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Financing income |  |  |  |  |  |  |  |  | 157 |  |
Total operating revenue |  |  |  |  |  |  |  |  | 157 | 132 | 120
Electric Utility | Operating Segments |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue recognized from contracts with customers |  |  |  |  |  |  |  |  | 4,528 |  |
Financing income |  |  |  |  |  |  |  |  | 10 |  |
Consumers alternative revenue programs |  |  |  |  |  |  |  |  | 23 |  |
Total operating revenue |  |  |  |  |  |  |  |  | 4,561 | 4,448 | 4,379
Gas Utility | Operating Segments |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue recognized from contracts with customers |  |  |  |  |  |  |  |  | 1,882 |  |
Financing income |  |  |  |  |  |  |  |  | 5 |  |
Consumers alternative revenue programs |  |  |  |  |  |  |  |  | 16 |  |
Total operating revenue |  |  |  |  |  |  |  |  | 1,903 | 1,774 | 1,685
Enterprises | Operating Segments |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue recognized from contracts with customers |  |  |  |  |  |  |  |  | 92 |  |
Leasing income |  |  |  |  |  |  |  |  | 160 |  |
Total operating revenue |  |  |  |  |  |  |  |  | 252 | 229 | 215
Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue recognized from contracts with customers |  |  |  |  |  |  |  |  | 6,410 |  |
Leasing income |  |  |  |  |  |  |  |  | 0 |  |
Financing income |  |  |  |  |  |  |  |  | 15 |  |
Consumers alternative revenue programs |  |  |  |  |  |  |  |  | 39 |  |
Total operating revenue | $ 1,712 | $ 1,502 | $ 1,395 | $ 1,855 | $ 1,686 | $ 1,437 | $ 1,362 | $ 1,737 | 6,464 | 6,222 | 6,064
Consumers Energy Company | Other reconciling items |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Total operating revenue |  |  |  |  |  |  |  |  | 0 |  |
Consumers Energy Company | Electric Utility | Operating Segments |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue recognized from contracts with customers |  |  |  |  |  |  |  |  | 4,528 |  |
Financing income |  |  |  |  |  |  |  |  | 10 |  |
Consumers alternative revenue programs |  |  |  |  |  |  |  |  | 23 |  |
Total operating revenue |  |  |  |  |  |  |  |  | 4,561 | 4,448 | 4,379
Consumers Energy Company | Gas Utility | Operating Segments |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue recognized from contracts with customers |  |  |  |  |  |  |  |  | 1,882 |  |
Financing income |  |  |  |  |  |  |  |  | 5 |  |
Consumers alternative revenue programs |  |  |  |  |  |  |  |  | 16 |  |
Total operating revenue |  |  |  |  |  |  |  |  | 1,903 | $ 1,774 | $ 1,685
Consumers Energy Company | Enterprises | Operating Segments |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Total operating revenue |  |  |  |  |  |  |  |  | 0 |  |
Residential | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue recognized from contracts with customers |  |  |  |  |  |  |  |  | 3,333 |  |
Residential | Consumers Energy Company | Electric Utility | Operating Segments |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue recognized from contracts with customers |  |  |  |  |  |  |  |  | 2,049 |  |
Residential | Consumers Energy Company | Gas Utility | Operating Segments |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue recognized from contracts with customers |  |  |  |  |  |  |  |  | 1,284 |  |
Commercial | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue recognized from contracts with customers |  |  |  |  |  |  |  |  | 1,912 |  |
Commercial | Consumers Energy Company | Electric Utility | Operating Segments |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue recognized from contracts with customers |  |  |  |  |  |  |  |  | 1,545 |  |
Commercial | Consumers Energy Company | Gas Utility | Operating Segments |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue recognized from contracts with customers |  |  |  |  |  |  |  |  | 367 |  |
Industrial | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue recognized from contracts with customers |  |  |  |  |  |  |  |  | 729 |  |
Industrial | Consumers Energy Company | Electric Utility | Operating Segments |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue recognized from contracts with customers |  |  |  |  |  |  |  |  | 674 |  |
Industrial | Consumers Energy Company | Gas Utility | Operating Segments |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue recognized from contracts with customers |  |  |  |  |  |  |  |  | 55 |  |
Other |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue recognized from contracts with customers |  |  |  |  |  |  |  |  | 92 |  |
Other | Enterprises | Operating Segments |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue recognized from contracts with customers |  |  |  |  |  |  |  |  | 92 |  |
Other | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue recognized from contracts with customers |  |  |  |  |  |  |  |  | 436 |  |
Other | Consumers Energy Company | Electric Utility | Operating Segments |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue recognized from contracts with customers |  |  |  |  |  |  |  |  | 260 |  |
Other | Consumers Energy Company | Gas Utility | Operating Segments |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue recognized from contracts with customers |  |  |  |  |  |  |  |  | $ 176 |  |

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