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Reportable Segments (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2017 | Jun. 30, 2016 | Jun. 30, 2017 | Jun. 30, 2016 | Dec. 31, 2016
Segment Reporting Information [Line Items] |  |  |  |  |  |
Operating Revenue |  | $ 1,449 | $ 1,371 | $ 3,278 | $ 3,172 |
Net Income Attributable to CMS Energy |  | 92 | 124 | 291 | 288 |
Plant, property, and equipment, gross |  | 21,628 |  | 21,628 |  | $ 21,010
Total Assets |  | 21,867 |  | 21,867 |  | 21,622
Consumers Energy Company [Member] |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Operating Revenue |  | 1,362 | 1,293 | 3,099 | 3,016 |
Net income available to common stockholder |  | 103 | 131 | 314 | 303 |
Plant, property, and equipment, gross |  | 21,451 |  | 21,451 |  | 20,838
Total Assets |  | 20,205 |  | 20,205 |  | 19,946
Electric Utility [Member] |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Operating Revenue |  | 1,077 | 1,022 | 2,113 | 2,035 |
Net Income Attributable to CMS Energy |  | 94 | 113 | 218 | 204 |
Plant, property, and equipment, gross | [1] | 14,937 |  | 14,937 |  | 14,540
Total Assets | [1] | 13,772 |  | 13,772 |  | 13,429
Electric Utility [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Operating Revenue |  | 1,077 | 1,022 | 2,113 | 2,035 |
Net income available to common stockholder |  | 94 | 113 | 218 | 204 |
Plant, property, and equipment, gross | [1] | 14,937 |  | 14,937 |  | 14,540
Total Assets | [1] | 13,774 |  | 13,774 |  | 13,430
Gas Utility [Member] |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Operating Revenue |  | 285 | 271 | 986 | 981 |
Net Income Attributable to CMS Energy |  | 9 | 18 | 96 | 99 |
Plant, property, and equipment, gross | [1] | 6,499 |  | 6,499 |  | 6,283
Total Assets | [1] | 6,393 |  | 6,393 |  | 6,446
Gas Utility [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Operating Revenue |  | 285 | 271 | 986 | 981 |
Net income available to common stockholder |  | 9 | 18 | 96 | 99 |
Plant, property, and equipment, gross | [1] | 6,499 |  | 6,499 |  | 6,283
Total Assets | [1] | 6,393 |  | 6,393 |  | 6,446
Enterprises [Member] |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Operating Revenue |  | 55 | 49 | 114 | 97 |
Net Income Attributable to CMS Energy |  | 7 | 3 | 19 | 9 |
Plant, property, and equipment, gross |  | 161 |  | 161 |  | 157
Total Assets |  | 270 |  | 270 |  | 269
Other reconciling items [Member] |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Operating Revenue |  | 32 | 29 | 65 | 59 |
Net Income Attributable to CMS Energy |  | (18) | $ (10) | (42) | $ (24) |
Plant, property, and equipment, gross |  | 31 |  | 31 |  | 30
Total Assets |  | 1,432 |  | 1,432 |  | 1,478
Other reconciling items [Member] | Consumers Energy Company [Member] |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |
Plant, property, and equipment, gross |  | 15 |  | 15 |  | 15
Total Assets |  | $ 38 |  | $ 38 |  | $ 70
[1] | Amounts include a portion of Consumers' other common assets attributable to both the electric and gas utility businesses.

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