Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 6,050,136	$ 5,806,680	$ 6,021,460	$ 5,752,793
OCI (loss) before reclassifications	(2,206)	(255)	(1,954)	7
Amounts reclassified from accumulated other comprehensive loss	1,100	1,189	2,001	2,211
Ending balance	6,021,523	5,834,899	6,021,523	5,834,899
APS
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	6,929,796	6,386,275	6,750,473	6,345,185
Ending balance	6,899,284	6,412,290	6,899,284	6,412,290
Pension and Other Postretirement Benefits
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(52,984)	(59,703)	(53,885)	(60,725)
OCI (loss) before reclassifications	(3,213)	(1,125)	(3,213)	(1,125)
Amounts reclassified from accumulated other comprehensive loss	1,100	1,189	2,001	2,211
Ending balance	(55,097)	(59,639)	(55,097)	(59,639)
Pension and Other Postretirement Benefits | APS
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(34,060)	(39,991)	(34,880)	(40,918)
OCI (loss) before reclassifications	(3,160)	(914)	(3,160)	(914)
Amounts reclassified from accumulated other comprehensive loss	999	1,073	1,819	2,000
Ending balance	(36,221)	(39,832)	(36,221)	(39,832)
Derivative Instruments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(724)	(1,809)	(976)	(2,071)
OCI (loss) before reclassifications	1,007	870	1,259	1,132
Amounts reclassified from accumulated other comprehensive loss	0	0	0	0
Ending balance	283	(939)	283	(939)
Accumulated Other Comprehensive Loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(53,708)	(61,512)	(54,861)	(62,796)
Ending balance	(54,814)	(60,578)	(54,814)	(60,578)
Accumulated Other Comprehensive Loss | APS
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(34,060)	(39,991)	(34,880)	(40,918)
Ending balance	$ (36,221)	$ (39,832)	$ (36,221)	$ (39,832)