Summary of Significant Accounting Policies - Summary of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Utility Plant and Depreciation [Line Items]
Net	$ 14,184,058	$ 13,727,575
Construction work in progress	1,329,478	937,384
Intangible assets, net of accumulated amortization	273,693	282,570
Nuclear fuel, net of accumulated amortization	106,039	113,645
Total property, plant and equipment	15,987,434	15,159,210
Electric Service
Utility Plant and Depreciation [Line Items]
Generation	9,480,572	9,199,012
Transmission	3,402,016	3,290,477
Distribution	7,520,016	7,107,007
General plant	1,286,057	1,241,389
Plant in service and held for future use	21,688,661	20,837,885
Accumulated depreciation and amortization	(7,504,603)	(7,110,310)
Net	14,184,058	13,727,575
Construction work in progress	1,329,478	937,384
Intangible assets, net of accumulated amortization	273,693	282,570
Nuclear fuel, net of accumulated amortization	106,039	113,645
Total property, plant and equipment	15,987,434	15,159,210
Electric Service | Variable Interest Entity
Utility Plant and Depreciation [Line Items]
Total property, plant and equipment	$ 94,166	$ 98,036