v3.26.1
Changes in Accumulated Other Comprehensive Loss (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Changes in accumulated other comprehensive income (loss) by component        
Beginning balance $ 7,110,968 $ 6,845,982 $ 7,087,075 $ 6,857,478
Ending balance 7,075,087 6,827,940 7,075,087 6,827,940
Accumulated Other Comprehensive Loss        
Changes in accumulated other comprehensive income (loss) by component        
Beginning balance (31,949) (30,094) (32,408) (30,942)
Other comprehensive income/(loss) before reclassifications 422 (797) 379 (447)
Amounts reclassified from accumulated other comprehensive loss 493 450 995 948
Ending balance (31,034) (30,441) (31,034) (30,441)
Pension and Other Postretirement Benefits        
Changes in accumulated other comprehensive income (loss) by component        
Beginning balance (32,478) (31,163) (32,980) (31,661)
Other comprehensive income/(loss) before reclassifications 404 (503) 404 (503)
Amounts reclassified from accumulated other comprehensive loss 493 450 995 948
Ending balance (31,581) (31,216) (31,581) (31,216)
Derivative Instruments        
Changes in accumulated other comprehensive income (loss) by component        
Beginning balance 529 1,069 572 719
Other comprehensive income/(loss) before reclassifications 18 (294) (25) 56
Amounts reclassified from accumulated other comprehensive loss 0 0 0 0
Ending balance 547 775 547 775
APS        
Changes in accumulated other comprehensive income (loss) by component        
Beginning balance 8,976,612 8,381,322 8,922,255 8,376,332
Ending balance 9,045,321 8,665,366 9,045,321 8,665,366
APS | Accumulated Other Comprehensive Loss        
Changes in accumulated other comprehensive income (loss) by component        
Beginning balance (15,047) (13,710) (15,457) (14,116)
Ending balance (14,187) (13,846) (14,187) (13,846)
APS | Pension and Other Postretirement Benefits        
Changes in accumulated other comprehensive income (loss) by component        
Beginning balance (15,047) (13,710) (15,457) (14,116)
Other comprehensive income/(loss) before reclassifications 454 (504) 454 (504)
Amounts reclassified from accumulated other comprehensive loss 406 368 816 774
Ending balance $ (14,187) $ (13,846) $ (14,187) $ (13,846)