Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 6,310,533	$ 6,164,451	$ 6,284,862	$ 6,159,876
OCI (loss) before reclassifications	(1,177)	(536)	(1,177)	(1,152)
Amounts reclassified from accumulated other comprehensive loss	465	481	1,027	996
Ending balance	6,316,322	6,076,137	6,316,322	6,076,137
APS
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	7,369,047	7,218,379	7,349,136	7,052,955
Ending balance	7,824,320	7,134,586	7,824,320	7,134,586
Accumulated Other Comprehensive Loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(32,582)	(31,536)	(33,144)	(31,435)
Ending balance	(33,294)	(31,591)	(33,294)	(31,591)
Accumulated Other Comprehensive Loss | APS
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(16,729)	(15,139)	(17,219)	(15,596)
Ending balance	(17,036)	(15,547)	(17,036)	(15,547)
Pension and Other Postretirement Benefits
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(34,192)	(31,817)	(34,754)	(32,332)
OCI (loss) before reclassifications	(778)	(982)	(778)	(982)
Amounts reclassified from accumulated other comprehensive loss	465	481	1,027	996
Ending balance	(34,505)	(32,318)	(34,505)	(32,318)
Pension and Other Postretirement Benefits | APS
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(16,729)	(15,139)	(17,219)	(15,596)
OCI (loss) before reclassifications	(717)	(839)	(717)	(839)
Amounts reclassified from accumulated other comprehensive loss	410	431	900	888
Ending balance	(17,036)	(15,547)	(17,036)	(15,547)
Derivative Instruments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	1,610	281	1,610	897
OCI (loss) before reclassifications	(399)	446	(399)	(170)
Amounts reclassified from accumulated other comprehensive loss	0	0	0	0
Ending balance	$ 1,211	$ 727	$ 1,211	$ 727