Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Changes in accumulated other comprehensive income (loss) by component
Beginning balance	$ 6,857,478	$ 6,284,862
Ending balance	7,087,075	6,857,478
Accumulated Other Comprehensive Loss
Changes in accumulated other comprehensive income (loss) by component
Beginning balance	(30,942)	(33,144)
Other comprehensive income/(loss) before reclassifications	(3,357)	148
Amounts reclassified from accumulated other comprehensive loss	1,891	2,054
Ending balance	(32,408)	(30,942)
Pension and Other Postretirement Benefits
Changes in accumulated other comprehensive income (loss) by component
Beginning balance	(31,661)	(34,754)
Other comprehensive income/(loss) before reclassifications	(3,210)	1,039
Amounts reclassified from accumulated other comprehensive loss	1,891	2,054
Ending balance	(32,980)	(31,661)
Derivative Instruments
Changes in accumulated other comprehensive income (loss) by component
Beginning balance	719	1,610
Other comprehensive income/(loss) before reclassifications	(147)	(891)
Amounts reclassified from accumulated other comprehensive loss	0	0
Ending balance	572	719
APS
Changes in accumulated other comprehensive income (loss) by component
Beginning balance	8,376,332	7,349,136
Ending balance	8,922,255	8,376,332
APS | Accumulated Other Comprehensive Loss
Changes in accumulated other comprehensive income (loss) by component
Beginning balance	(14,116)	(17,219)
Ending balance	(15,457)	(14,116)
APS | Pension and Other Postretirement Benefits
Changes in accumulated other comprehensive income (loss) by component
Beginning balance	(14,116)	(17,219)
Other comprehensive income/(loss) before reclassifications	(2,889)	1,255
Amounts reclassified from accumulated other comprehensive loss	1,548	1,848
Ending balance	$ (15,457)	$ (14,116)