| In millions, except per share items | Dec-31-21 | Dec-31-20 | Dec-31-19 | Dec-31-18 | Dec-31-17 | Dec-31-16 | Dec-31-15 | Dec-31-14 |
| | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K/A | 10-K |
| Operating Revenues | | | | | | | | |
| Total Operating Revenues | 1,197.6 | 883.2 | 918.5 | 916.4 | 849.4 | 803.5 | | 799.3 |
| Total Operating Revenues growth | 35.6% | -3.8% | 0.2% | 7.9% | 5.7% | | | 7.5% |
| Operating Expenses | | | | | | | | |
| Other Nonelectric Expenses | 65.4 | 55.1 | 50.8 | 51.5 | 41.5 | 38.7 | | 46.0 |
| Depreciation and Amortization | 91.4 | 82.0 | 78.1 | 74.7 | 72.5 | 73.4 | | 58.1 |
| Total Operating Expenses | 947.1 | 742.2 | 784.6 | 787.1 | 717.1 | 686.9 | | 699.7 |
| Operating Income | 249.7 | 147.9 | 134.9 | 129.4 | 132.3 | 116.6 | | 99.5 |
| Operating margin | 20.9% | 16.7% | 14.7% | 14.1% | 15.6% | 14.5% | | 12.5% |
| |
| Other Income and Expense | | | | | | | | |
| Interest Charges | -37.8 | -34.4 | -31.4 | -30.4 | -29.6 | -31.9 | | -29.6 |
| Nonservice Cost Components of Postretirement Benefits | 2.0 | 3.4 | 4.3 | 5.5 | 5.6 | 5.1 | | |
| Other Income (Expense), net | 2.9 | 6.1 | 5.1 | 3.5 | 2.6 | 2.9 | | 3.6 |
| Income Before Income Taxes | 212.8 | 116.1 | 104.3 | 96.9 | 99.7 | 82.5 | | 73.4 |
| Income Tax Expense | 36.1 | 20.2 | 17.4 | 14.6 | 27.3 | 20.2 | | 16.6 |
| Net Income | 176.8 | 95.9 | 86.8 | 82.3 | 72.4 | 62.3 | | 57.7 |
| |
| Weighted-Average Common Shares Outstanding: | | | | | | | | |
| Basic (in shares) | 41.5 | 40.7 | 39.7 | 39.6 | 39.5 | 38.5 | | 36.5 |
| Diluted (in shares) | 41.8 | 40.9 | 40.0 | 39.9 | 39.7 | 38.7 | | 36.8 |
| |
| Earnings Per Share: | | | | | | | | |
| Basic (in dollars per share) | $4.26 | $2.35 | $2.19 | $2.08 | $1.84 | $1.62 | | $1.58 |
| Diluted (in dollars per share) | $4.23 | $2.34 | $2.17 | $2.06 | $1.82 | $1.61 | | $1.57 |