| In millions, except per share items | Dec-31-22 | Dec-31-21 | Dec-31-20 | Dec-31-19 | Dec-31-18 | Dec-31-17 | Dec-31-16 | Dec-31-15 |
| | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K | 10-K |
| Operating activities | | | | | | | | |
| Net income | 221.7 | 206.4 | 196.4 | 186.7 | 172.2 | 163.0 | 140.1 | 119.0 |
| |
| Adjustments to reconcile net income to net cash from operating activities: | | | | | | | | |
| Depreciation and amortization | 228.5 | 207.2 | 194.9 | 180.4 | 160.1 | 151.9 | 143.8 | 133.0 |
| Deferred income taxes | -22.0 | 43.4 | 18.5 | 13.3 | 53.2 | 92.4 | 86.8 | 63.8 |
| Share-based compensation expense | 10.7 | 10.5 | 9.8 | 9.3 | 8.2 | 8.9 | 11.2 | 9.2 |
| Provision for doubtful accounts | 6.0 | 9.1 | 15.5 | 9.0 | 8.5 | 7.3 | 5.4 | 4.5 |
| Proceeds from Securitization Bonds, Operating Activities | 1,330.6 | | | | | | | |
| Changes in assets and liabilities: | | | | | | | | |
| Accounts receivable | -213.7 | -57.9 | -58.4 | 30.4 | 0.8 | -15.1 | -80.0 | 105.9 |
| Materials and supplies | -16.0 | -2.1 | 3.0 | -11.4 | -4.7 | -5.6 | -0.8 | -5.8 |
| Natural gas in storage | -89.6 | -85.7 | 10.3 | 3.0 | 22.9 | -4.7 | 16.7 | 43.1 |
| Asset removal costs | -47.0 | -49.0 | -40.8 | | | | | |
| Accounts payable | 85.9 | 107.2 | 28.4 | -59.3 | 36.9 | 1.9 | 27.6 | -59.6 |
| Accrued taxes other than income | 11.3 | 3.2 | 15.8 | 0.3 | 6.3 | -1.2 | 5.3 | -7.5 |
| Customer deposits | -4.6 | -5.6 | 10.0 | -3.2 | 0.4 | -0.4 | 0.9 | 0.3 |
| Increase Decrease In Regulatory Assets And Liabilities Current | 52.4 | -1,562.6 | -38.8 | | | | | |
| Increase Decrease In Regulatory Assets And Liabilities Non-current | 54.0 | -367.2 | 23.6 | | | | | |
| Employee benefit obligation | | | -3.1 | -35.4 | -50.1 | -118.1 | -25.7 | -15.0 |
| Increase (Decrease) in Other Current Assets and Liabilities, Net | -23.4 | 18.5 | -12.9 | 7.2 | -1.9 | | | |
| Increase (Decrease) in Other Noncurrent Assets and Liabilities, Net | -14.1 | -11.2 | -7.7 | -0.5 | | | | |
| Cash provided by (used in) operating activities | 1,570.8 | -1,535.7 | 364.5 | 310.3 | 467.7 | 253.8 | 290.6 | 407.9 |
| |
| Investing activities | | | | | | | | |
| Payments to Acquire Property, Plant, and Equipment | -609.5 | -495.2 | -471.3 | -417.3 | -394.5 | -356.4 | -309.1 | -294.3 |
| Payments for (Proceeds from) Other Investing Activities | -8.6 | -7.6 | -2.8 | | | 0.6 | | |
| Proceeds from Sale of Other Assets, Investing Activities | 4.0 | 1.7 | 3.8 | 1.4 | | | | |
| Net Cash Provided by (Used in) Investing Activities | -614.1 | -501.1 | -470.4 | -422.9 | -394.5 | -355.7 | -308.6 | -294.3 |
| |
| Financing activities | | | | | | | | |
| Proceeds from (Repayments of) Notes Payable | 58.0 | 75.8 | -98.3 | | | | | |
| Proceeds from Issuance of Other Long-Term Debt | 297.6 | 2,498.9 | 298.4 | | 395.6 | | | |
| Proceeds from Securitization Bonds, Financing Activities | 335.9 | | | | | | | |
| Payments of Debt Issuance Costs | -8.6 | -35.1 | -2.9 | | -4.3 | | | |
| Issuance of common stock | 133.7 | 26.7 | 19.4 | 5.1 | 4.8 | 4.5 | 4.0 | 7.1 |
| Repayments of Long-term Debt | -1,627.0 | -400.0 | | | -300.0 | | | |
| Dividends paid | -134.0 | -123.9 | -114.4 | -105.4 | -96.6 | -88.0 | -73.2 | -62.8 |
| Payment, Tax Withholding, Share-Based Payment Arrangement | -3.2 | -4.7 | -6.3 | | | | | |
| Cash provided by (used in) financing activities | -947.5 | 2,037.6 | 96.0 | 109.1 | -66.3 | 101.7 | 30.2 | -123.1 |
| Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect | 9.3 | 0.9 | -9.9 | | | | | |
| |
| Cash, cash equivalents, restricted cash and restricted cash equivalents at beginning of period | | | | | | | | |
| Cash, cash equivalents, restricted cash and restricted cash equivalents at end of period | | | | | | | | |
| Supplemental cash flow information: | | | | | | | | |
| Interest Paid, Excluding Capitalized Interest, Operating Activities | 84.9 | 70.1 | 60.1 | 61.2 | 49.4 | 44.4 | 42.1 | 43.0 |
| Cash paid (received) for income taxes, net | 67.4 | -10.8 | 30.4 | 30.2 | 0.8 | -1.4 | -35.7 | -5.4 |