Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 6,284,862	$ 6,159,876
OCI (loss) before reclassifications	0	(616)
Amounts reclassified from accumulated other comprehensive loss	562	515
Ending balance	6,310,533	6,164,451
APS
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	7,349,136	7,052,955
Ending balance	7,369,047	7,218,379
Accumulated Other Comprehensive Loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(33,144)	(31,435)
Ending balance	(32,582)	(31,536)
Accumulated Other Comprehensive Loss | APS
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(17,219)	(15,596)
Ending balance	(16,729)	(15,139)
Pension and Other Postretirement Benefits
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(34,754)	(32,332)
OCI (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive loss	562	515
Ending balance	(34,192)	(31,817)
Pension and Other Postretirement Benefits | APS
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(17,219)	(15,596)
OCI (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive loss	490	457
Ending balance	(16,729)	(15,139)
Derivative Instruments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	1,610	897
OCI (loss) before reclassifications	0	(616)
Amounts reclassified from accumulated other comprehensive loss	0	0
Ending balance	$ 1,610	$ 281