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Reportable Segments (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
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating Revenue | $ 1,829 | $ 1,599 | $ 1,492 | $ 1,953 | $ 1,778 | $ 1,527 | $ 1,449 | $ 1,829 | $ 6,873 | $ 6,583 | $ 6,399
Depreciation and amortization |  |  |  |  |  |  |  |  | 933 | 881 | 811
Income from equity method investees |  |  |  |  |  |  |  |  | 9 | 15 | 13
Interest charges |  |  |  |  |  |  |  |  | 458 | 438 | 435
Income tax expense (benefit) |  |  |  |  |  |  |  |  | 115 | 424 | 273
Net income (loss) available to common stockholders | 108 | 169 | 139 | 241 | (3) | 172 | 92 | 199 | 657 | 460 | 551
Plant, property, and equipment, gross | 24,400 |  |  |  | 22,506 |  |  |  | 24,400 | 22,506 | 21,010
Investments in equity method investees | 69 |  |  |  | 64 |  |  |  | 69 | 64 | 65
Total assets | 24,529 |  |  |  | 23,050 |  |  |  | 24,529 | 23,050 | 21,622
Capital expenditures |  |  |  |  |  |  |  |  | 2,081 | 1,722 | 1,633
Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating Revenue | 1,712 | 1,502 | 1,395 | 1,855 | 1,686 | 1,437 | 1,362 | 1,737 | 6,464 | 6,222 | 6,064
Depreciation and amortization |  |  |  |  |  |  |  |  | 921 | 872 | 803
Interest charges |  |  |  |  |  |  |  |  | 289 | 276 | 268
Income tax expense (benefit) |  |  |  |  |  |  |  |  | 142 | 339 | 320
Net income available to common stockholder | 130 | $ 180 | $ 151 | $ 242 | 135 | $ 181 | $ 103 | $ 211 | 703 | 630 | 614
Plant, property, and equipment, gross | 23,963 |  |  |  | 22,318 |  |  |  | 23,963 | 22,318 | 20,838
Total assets | 22,025 |  |  |  | 21,099 |  |  |  | 22,025 | 21,099 | 19,946
Capital expenditures |  |  |  |  |  |  |  |  | 1,825 | 1,683 | 1,618
Other reconciling items |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating Revenue |  |  |  |  |  |  |  |  | 157 | 132 | 120
Depreciation and amortization |  |  |  |  |  |  |  |  | 4 | 3 | 3
Interest charges |  |  |  |  |  |  |  |  | 168 | 163 | 166
Income tax expense (benefit) |  |  |  |  |  |  |  |  | (29) | 11 | (57)
Net income (loss) available to common stockholders |  |  |  |  |  |  |  |  | (81) | (141) | (79)
Plant, property, and equipment, gross | 42 |  |  |  | 38 |  |  |  | 42 | 38 | 30
Investments in equity method investees | 0 |  |  |  | 0 |  |  |  | 0 | 0 | 3
Total assets | 2,104 |  |  |  | 1,663 |  |  |  | 2,104 | 1,663 | 1,478
Capital expenditures |  |  |  |  |  |  |  |  | 12 | 7 | 5
Other reconciling items | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating Revenue |  |  |  |  |  |  |  |  | 0 |  |
Interest charges |  |  |  |  |  |  |  |  | 1 | 1 | 0
Income tax expense (benefit) |  |  |  |  |  |  |  |  | 0 | (2) | 0
Net income available to common stockholder |  |  |  |  |  |  |  |  | (1) | 2 | 1
Plant, property, and equipment, gross | 17 |  |  |  | 17 |  |  |  | 17 | 17 | 15
Total assets | 29 |  |  |  | 53 |  |  |  | 29 | 53 | 70
Capital expenditures |  |  |  |  |  |  |  |  | 2 | 1 | 0
Electric Utility | Operating Segments |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating Revenue |  |  |  |  |  |  |  |  | 4,561 | 4,448 | 4,379
Depreciation and amortization |  |  |  |  |  |  |  |  | 682 | 654 | 603
Interest charges |  |  |  |  |  |  |  |  | 209 | 201 | 196
Income tax expense (benefit) |  |  |  |  |  |  |  |  | 109 | 245 | 246
Net income (loss) available to common stockholders |  |  |  |  |  |  |  |  | 535 | 455 | 458
Plant, property, and equipment, gross | 16,027 |  |  |  | 15,221 |  |  |  | 16,027 | 15,221 | 14,540
Total assets | 14,079 |  |  |  | 13,906 |  |  |  | 14,079 | 13,906 | 13,429
Capital expenditures |  |  |  |  |  |  |  |  | 865 | 882 | 1,007
Electric Utility | Operating Segments | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating Revenue |  |  |  |  |  |  |  |  | 4,561 | 4,448 | 4,379
Depreciation and amortization |  |  |  |  |  |  |  |  | 682 | 654 | 603
Interest charges |  |  |  |  |  |  |  |  | 209 | 201 | 196
Income tax expense (benefit) |  |  |  |  |  |  |  |  | 109 | 245 | 246
Net income available to common stockholder |  |  |  |  |  |  |  |  | 535 | 455 | 458
Plant, property, and equipment, gross | 16,027 |  |  |  | 15,221 |  |  |  | 16,027 | 15,221 | 14,540
Total assets | 14,143 |  |  |  | 13,907 |  |  |  | 14,143 | 13,907 | 13,430
Capital expenditures |  |  |  |  |  |  |  |  | 865 | 882 | 1,007
Gas Utility | Operating Segments |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating Revenue |  |  |  |  |  |  |  |  | 1,903 | 1,774 | 1,685
Depreciation and amortization |  |  |  |  |  |  |  |  | 239 | 218 | 200
Interest charges |  |  |  |  |  |  |  |  | 79 | 74 | 72
Income tax expense (benefit) |  |  |  |  |  |  |  |  | 33 | 96 | 74
Net income (loss) available to common stockholders |  |  |  |  |  |  |  |  | 169 | 173 | 155
Plant, property, and equipment, gross | 7,919 |  |  |  | 7,080 |  |  |  | 7,919 | 7,080 | 6,283
Total assets | 7,806 |  |  |  | 7,139 |  |  |  | 7,806 | 7,139 | 6,446
Capital expenditures |  |  |  |  |  |  |  |  | 958 | 800 | 611
Gas Utility | Operating Segments | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating Revenue |  |  |  |  |  |  |  |  | 1,903 | 1,774 | 1,685
Depreciation and amortization |  |  |  |  |  |  |  |  | 239 | 218 | 200
Interest charges |  |  |  |  |  |  |  |  | 79 | 74 | 72
Income tax expense (benefit) |  |  |  |  |  |  |  |  | 33 | 96 | 74
Net income available to common stockholder |  |  |  |  |  |  |  |  | 169 | 173 | 155
Plant, property, and equipment, gross | 7,919 |  |  |  | 7,080 |  |  |  | 7,919 | 7,080 | 6,283
Total assets | 7,853 |  |  |  | 7,139 |  |  |  | 7,853 | 7,139 | 6,446
Capital expenditures |  |  |  |  |  |  |  |  | 958 | 800 | 611
Enterprises | Operating Segments |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating Revenue |  |  |  |  |  |  |  |  | 252 | 229 | 215
Depreciation and amortization |  |  |  |  |  |  |  |  | 8 | 6 | 5
Income from equity method investees |  |  |  |  |  |  |  |  | 9 | 15 | 13
Interest charges |  |  |  |  |  |  |  |  | 2 | 0 | 1
Income tax expense (benefit) |  |  |  |  |  |  |  |  | 2 | 72 | 10
Net income (loss) available to common stockholders |  |  |  |  |  |  |  |  | 34 | (27) | 17
Plant, property, and equipment, gross | 412 |  |  |  | 167 |  |  |  | 412 | 167 | 157
Investments in equity method investees | 69 |  |  |  | 64 |  |  |  | 69 | 64 | 62
Total assets | $ 540 |  |  |  | $ 342 |  |  |  | 540 | 342 | 269
Capital expenditures |  |  |  |  |  |  |  |  | 246 | $ 33 | $ 10
Enterprises | Operating Segments | Consumers Energy Company |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating Revenue |  |  |  |  |  |  |  |  | $ 0 |  |

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