Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Changes in accumulated other comprehensive income (loss) by component
Beginning balance	$ 6,845,982	$ 6,310,533	$ 6,857,478	$ 6,284,862
Ending balance	6,827,940	6,316,322	6,827,940	6,316,322
Accumulated Other Comprehensive Loss
Changes in accumulated other comprehensive income (loss) by component
Beginning balance	(30,094)	(32,582)	(30,942)	(33,144)
Other comprehensive income (loss) before reclassifications	(797)	(1,177)	(447)	(1,177)
Amounts reclassified from accumulated other comprehensive loss	450	465	948	1,027
Ending balance	(30,441)	(33,294)	(30,441)	(33,294)
Pension and Other Postretirement Benefits
Changes in accumulated other comprehensive income (loss) by component
Beginning balance	(31,163)	(34,192)	(31,661)	(34,754)
Other comprehensive income (loss) before reclassifications	(503)	(778)	(503)	(778)
Amounts reclassified from accumulated other comprehensive loss	450	465	948	1,027
Ending balance	(31,216)	(34,505)	(31,216)	(34,505)
Derivative Instruments
Changes in accumulated other comprehensive income (loss) by component
Beginning balance	1,069	1,610	719	1,610
Other comprehensive income (loss) before reclassifications	(294)	(399)	56	(399)
Amounts reclassified from accumulated other comprehensive loss	0	0	0	0
Ending balance	775	1,211	775	1,211
APS
Changes in accumulated other comprehensive income (loss) by component
Beginning balance	8,381,322	7,369,047	8,376,332	7,349,136
Ending balance	8,665,366	7,824,320	8,665,366	7,824,320
APS | Accumulated Other Comprehensive Loss
Changes in accumulated other comprehensive income (loss) by component
Beginning balance	(13,710)	(16,729)	(14,116)	(17,219)
Ending balance	(13,846)	(17,036)	(13,846)	(17,036)
APS | Pension and Other Postretirement Benefits
Changes in accumulated other comprehensive income (loss) by component
Beginning balance	(13,710)	(16,729)	(14,116)	(17,219)
Other comprehensive income (loss) before reclassifications	(504)	(717)	(504)	(717)
Amounts reclassified from accumulated other comprehensive loss	368	410	774	900
Ending balance	$ (13,846)	$ (17,036)	$ (13,846)	$ (17,036)