Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Changes in accumulated other comprehensive income (loss) by component
Beginning balance	$ 7,087,075	$ 6,857,478
Ending balance	7,110,968	6,845,982
Accumulated Other Comprehensive Loss
Changes in accumulated other comprehensive income (loss) by component
Beginning balance	(32,408)	(30,942)
Other comprehensive income (loss) before reclassifications	(43)	350
Amounts reclassified from accumulated other comprehensive loss	502	498
Ending balance	(31,949)	(30,094)
Pension and Other Postretirement Benefits
Changes in accumulated other comprehensive income (loss) by component
Beginning balance	(32,980)	(31,661)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive loss	502	498
Ending balance	(32,478)	(31,163)
Derivative Instruments
Changes in accumulated other comprehensive income (loss) by component
Beginning balance	572	719
Other comprehensive income (loss) before reclassifications	(43)	350
Amounts reclassified from accumulated other comprehensive loss	0	0
Ending balance	529	1,069
APS
Changes in accumulated other comprehensive income (loss) by component
Beginning balance	8,922,255	8,376,332
Ending balance	8,976,612	8,381,322
APS | Accumulated Other Comprehensive Loss
Changes in accumulated other comprehensive income (loss) by component
Beginning balance	(15,457)	(14,116)
Ending balance	(15,047)	(13,710)
APS | Pension and Other Postretirement Benefits
Changes in accumulated other comprehensive income (loss) by component
Beginning balance	(15,457)	(14,116)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive loss	410	406
Ending balance	$ (15,047)	$ (13,710)