| In millions, except per share items | Jun-30-22 | Mar-31-22 | Dec-31-21 | Sep-30-21 | Jun-30-21 | Mar-31-21 | Dec-31-20 | Sep-30-20 |
| | 10-Q | 10-Q | 10-K | 10-Q | 10-Q | 10-Q | 10-K | 10-Q |
| Operating revenues | 937.0 | 842.0 | 951.0 | 1,092.0 | 999.0 | 888.0 | 923.0 | 1,079.0 |
| |
| Operating expenses: | | | | | | | | |
| Operation and maintenance | 376.0 | 364.0 | 491.0 | 436.0 | 431.0 | 419.0 | 429.0 | 419.0 |
| Depreciation and amortization | 163.0 | 158.0 | 160.0 | 161.0 | 158.0 | 157.0 | 153.0 | 154.0 |
| General taxes | 71.0 | 74.0 | 80.0 | 78.0 | 80.0 | 83.0 | 78.0 | 73.0 |
| Total operating expenses, net | 610.0 | 596.0 | 731.0 | 675.0 | 669.0 | 659.0 | 660.0 | 646.0 |
| Operating income | 327.0 | 246.0 | 220.0 | 417.0 | 330.0 | 229.0 | 263.0 | 433.0 |
| |
| Other income (expense): | | | | | | | | |
| Interest expense | -106.0 | -100.0 | -103.0 | -101.0 | -101.0 | -98.0 | -101.0 | -99.0 |
| Interest income | 12.0 | 13.0 | | | | | | |
| Non-operating benefit costs, net | 20.0 | 19.0 | 19.0 | 20.0 | 19.0 | 20.0 | 12.0 | 12.0 |
| Other, net | 17.0 | 15.0 | 7.0 | 4.0 | 3.0 | 4.0 | 5.0 | 6.0 |
| Total other (expense) income | -57.0 | -53.0 | 1,439.0 | -77.0 | -79.0 | -74.0 | -82.0 | -81.0 |
| Income before income taxes | 270.0 | 193.0 | 894.0 | 340.0 | 251.0 | 155.0 | 181.0 | 352.0 |
| Provision for income taxes | 52.0 | 35.0 | 249.0 | 62.0 | 44.0 | 22.0 | 36.0 | 88.0 |
| Net income attributable to common shareholders | 218.0 | 158.0 | 645.0 | 278.0 | 207.0 | 133.0 | 145.0 | 264.0 |
| |
| Basic earnings per share: | | | | | | | | |
| Net income attributable to common shareholders (dollars per share) | $1.20 | $0.87 | $3.56 | $1.53 | $1.14 | $0.73 | $0.80 | $1.46 |
| |
| Diluted earnings per share: | | | | | | | | |
| Net income attributable to common shareholders (dollars per share) | $1.20 | $0.87 | $3.55 | $1.53 | $1.14 | $0.73 | $0.80 | $1.46 |
| |
| Weighted-average common shares outstanding: | | | | | | | | |
| Basic (in shares) | 182.0 | 182.0 | 182.0 | 182.0 | 182.0 | 181.0 | 181.0 | 181.0 |
| Diluted (in shares) | 182.0 | 182.0 | 182.0 | 182.0 | 182.0 | 182.0 | 182.0 | 182.0 |