| In millions, except per share items | Sep-30-17 | Jun-30-17 | Mar-31-17 | Dec-31-16 | Sep-30-16 | Jun-30-16 | Mar-31-16 | Dec-31-15 |
| | 10-Q | 10-Q | 10-Q | 8-K | 10-Q | 10-Q | 10-Q | 8-K |
| Revenues | 1,437.0 | 1,164.0 | 1,247.0 | 1,107.0 | 1,184.0 | 904.0 | 1,123.0 | 1,016.0 |
| Cost of sales, excluding depreciation expense | -787.0 | -681.0 | -757.0 | 1,698.0 | -660.0 | -493.0 | -545.0 | 1,494.0 |
| Gross margin | 650.0 | 483.0 | 490.0 | 524.0 | 524.0 | 411.0 | 578.0 | 482.0 |
| Operating and maintenance expense | -236.0 | -282.0 | -232.0 | 695.0 | -218.0 | -256.0 | -221.0 | 580.0 |
| Depreciation expense | -202.0 | | | | -163.0 | | | |
| Impairments | 29.0 | 99.0 | 20.0 | 1.0 | 212.0 | 645.0 | | 25.0 |
| Loss on sale of assets, net | 78.0 | 29.0 | | | | | | |
| General and administrative expense | 44.0 | 42.0 | 40.0 | 44.0 | 41.0 | 39.0 | 37.0 | 34.0 |
| Acquisition and integration costs | 3.0 | 7.0 | 45.0 | 3.0 | 7.0 | 3.0 | 4.0 | 3.0 |
| Other | | 3.0 | -2.0 | 16.0 | | -16.0 | | 1.0 |
| Operating income (loss) | 58.0 | -182.0 | -49.0 | 34.0 | -117.0 | -702.0 | 145.0 | -13.0 |
| Bankruptcy reorganization items (Note 20) | 12.0 | -1.0 | 483.0 | | | | | |
| Earnings from unconsolidated investments | 4.0 | | | | 4.0 | | | |
| Interest expense | -161.0 | | | | -166.0 | | | |
| Loss on early extinguishment of debt (Note 13) | -66.0 | | | | | | | |
| Other income and expense, net | 19.0 | 29.0 | 17.0 | 5.0 | 29.0 | 30.0 | 1.0 | 9.0 |
| Loss before income taxes | -134.0 | | | | -250.0 | | | |
| Income tax benefit (Note 14) | 1.0 | 16.0 | 313.0 | 51.0 | 1.0 | 9.0 | -16.0 | 1.0 |
| Net income (loss) | -133.0 | -296.0 | 596.0 | 1,062.0 | -249.0 | -803.0 | -10.0 | |
| Less: Net loss attributable to noncontrolling interest | -1.0 | | -1.0 | -2.0 | | -2.0 | | |
| Net income (loss) attributable to Dynegy Inc. | -132.0 | -296.0 | 597.0 | -184.0 | -249.0 | -801.0 | -10.0 | -137.0 |
| Less: Dividends on preferred stock | 5.0 | | | | 5.0 | | | |
| Net income (loss) attributable to Dynegy Inc. common stockholders | -137.0 | -302.0 | 592.0 | 1,076.0 | -254.0 | -807.0 | -15.0 | |
| |
| Earnings (Loss) Per Share (Note 15): | | | | | | | | |
| Basic and diluted earnings (loss) per share attributable to Dynegy Inc. common stockholders: | | | | | | | | |
| Basic earnings | ($0.89) | ($1.96) | $4.00 | ($1.24) | ($1.81) | ($6.73) | ($0.13) | $48.67 |
| Diluted earnings | ($0.89) | ($1.96) | $3.57 | ($1.24) | ($1.81) | ($6.73) | ($0.13) | $26.69 |
| |
| Basic shares outstanding (in shares) | 154.0 | 154.0 | 148.0 | 129.0 | 140.0 | 120.0 | 117.0 | 0.1 |
| Diluted shares outstanding (in shares) | 154.0 | 154.0 | 167.0 | 129.0 | 140.0 | 120.0 | 117.0 | 0.1 |