Changes in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 6,021,460	$ 5,752,793
OCI before reclassifications	252	262
Amounts reclassified from accumulated other comprehensive loss	901	1,022
Ending balance	6,050,136	5,806,680
APS
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	6,750,473	6,345,185
Amounts reclassified from accumulated other comprehensive loss	820	927
Ending balance	6,929,796	6,386,275
Pension and Other Postretirement Benefits
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(53,885)	(60,725)
OCI before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive loss	901	1,022
Ending balance	(52,984)	(59,703)
Pension and Other Postretirement Benefits | APS
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(34,880)	(40,918)
Amounts reclassified from accumulated other comprehensive loss	820	927
Ending balance	(34,060)	(39,991)
Derivative Instruments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(976)	(2,071)
OCI before reclassifications	252	262
Amounts reclassified from accumulated other comprehensive loss	0	0
Ending balance	(724)	(1,809)
Accumulated Other Comprehensive Income (Loss)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(54,861)	(62,796)
Ending balance	(53,708)	(61,512)
Accumulated Other Comprehensive Income (Loss) | APS
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(34,880)	(40,918)
Ending balance	$ (34,060)	$ (39,991)