SCHEDULE I CONDENSED FINANCIAL INFORMATION OF PUGET ENERGY Notes (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
Net income									$ 235,622	$ 175,194	$ 312,899
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									182,702	184,624	306,453
Net Cash Provided by (Used in) Operating Activities									904,181	972,131	729,290
Net Cash Provided by (Used in) Investing Activities									(1,070,573)	(1,040,330)	(708,365)
Parent Company [Member]
Net income	$ 107,053	$ (21,970)	$ 3,642	$ 146,897	$ (467)	$ 12,836	$ 35,275	$ 127,550	235,622	175,194	312,899
Goodwill, Purchase Accounting Adjustments									4,700	3,900	5,200
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									182,702	184,624	306,453
Net Cash Provided by (Used in) Operating Activities									79,176	139,005	145,719
Net Cash Provided by (Used in) Investing Activities									(59,864)	(102,814)	(6,078)
Subsidiaries [Member]
Net income	$ 123,456	$ 3,891	$ 26,778	$ 163,037	$ 97,208	$ 29,100	$ 50,654	$ 143,092	317,162	320,054	380,581
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									253,184	338,659	384,620
Net Cash Provided by (Used in) Operating Activities									995,904	1,086,803	818,916
Net Cash Provided by (Used in) Investing Activities									$ (1,008,409)	$ (963,411)	$ (676,956)