Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 6,316,322	$ 6,076,137	$ 6,284,862	$ 6,159,876
OCI (loss) before reclassifications	(33)	659	(1,211)	(493)
Amounts reclassified from accumulated other comprehensive loss	513	498	1,541	1,494
Ending balance	6,726,070	6,488,205	6,726,070	6,488,205
APS
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	7,824,320	7,134,586	7,349,136	7,052,955
Ending balance	8,236,800	7,541,156	8,236,800	7,541,156
Accumulated Other Comprehensive Loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(33,294)	(31,591)	(33,144)	(31,435)
Ending balance	(32,814)	(30,434)	(32,814)	(30,434)
Accumulated Other Comprehensive Loss | APS
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(17,036)	(15,547)	(17,219)	(15,596)
Ending balance	(16,586)	(15,103)	(16,586)	(15,103)
Pension and Other Postretirement Benefits
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(34,505)	(32,318)	(34,754)	(32,332)
OCI (loss) before reclassifications	0	0	(779)	(982)
Amounts reclassified from accumulated other comprehensive loss	513	498	1,541	1,494
Ending balance	(33,992)	(31,820)	(33,992)	(31,820)
Pension and Other Postretirement Benefits | APS
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(17,036)	(15,547)	(17,219)	(15,596)
OCI (loss) before reclassifications	0	0	(718)	(839)
Amounts reclassified from accumulated other comprehensive loss	450	444	1,351	1,332
Ending balance	(16,586)	(15,103)	(16,586)	(15,103)
Derivative Instruments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	1,211	727	1,610	897
OCI (loss) before reclassifications	(33)	659	(432)	489
Amounts reclassified from accumulated other comprehensive loss	0	0	0	0
Ending balance	$ 1,178	$ 1,386	$ 1,178	$ 1,386