Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 6,076,137	$ 6,021,523	$ 6,159,876	$ 6,021,460
OCI (loss) before reclassifications	659	513	(493)	(1,441)
Amounts reclassified from accumulated other comprehensive loss	498	1,001	1,494	3,002
Ending balance	6,488,205	6,362,113	6,488,205	6,362,113
APS
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	7,134,586	6,899,284	7,052,955	6,750,473
Ending balance	7,541,156	7,236,194	7,541,156	7,236,194
Accumulated Other Comprehensive Loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(31,591)	(54,814)	(31,435)	(54,861)
Ending balance	(30,434)	(53,300)	(30,434)	(53,300)
Accumulated Other Comprehensive Loss | APS
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(15,547)	(36,221)	(15,596)	(34,880)
Ending balance	(15,103)	(35,312)	(15,103)	(35,312)
Pension and Other Postretirement Benefits
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(32,318)	(55,097)	(32,332)	(53,885)
OCI (loss) before reclassifications	0	0	(982)	(3,213)
Amounts reclassified from accumulated other comprehensive loss	498	1,001	1,494	3,002
Ending balance	(31,820)	(54,096)	(31,820)	(54,096)
Pension and Other Postretirement Benefits | APS
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(15,547)	(36,221)	(15,596)	(34,880)
OCI (loss) before reclassifications	0	0	(839)	(3,160)
Amounts reclassified from accumulated other comprehensive loss	444	909	1,332	2,728
Ending balance	(15,103)	(35,312)	(15,103)	(35,312)
Derivative Instruments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	727	283	897	(976)
OCI (loss) before reclassifications	659	513	489	1,772
Amounts reclassified from accumulated other comprehensive loss	0	0	0	0
Ending balance	$ 1,386	$ 796	$ 1,386	$ 796