SCHEDULE I CONDENSED FINANCIAL INFORMATION OF PUGET ENERGY - Condensed Statements of Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Non-utility expense and other									$ (54,519)	$ (53,864)	$ (42,620)
Non-hedged interest rate swap expense									0	28	(1,062)
Interest expense									(343,795)	(354,802)	(355,139)
Income taxes									(30,092)	(255,143)	(140,204)
Net income (loss)									235,622	175,194	312,899
Comprehensive income (loss)									182,702	184,624	306,453
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Non-utility expense and other									(1,345)	(1,466)	(5,252)
Equity In Net Income (Loss) Of Subsidiaries									320,122	323,568	385,838
Non-hedged interest rate swap expense									0	28	(1,062)
Interest income									4,273	1,039	2
Interest expense									(108,816)	(106,072)	(104,600)
Income taxes									21,388	(41,903)	37,973
Net income (loss)	$ 107,053	$ (21,970)	$ 3,642	$ 146,897	$ (467)	$ 12,836	$ 35,275	$ 127,550	235,622	175,194	312,899
Comprehensive income (loss)									$ 182,702	$ 184,624	$ 306,453