SCHEDULE I CONDENSED FINANCIAL INFORMATION OF PUGET ENERGY - Condensed Statements of Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Nonutility Expense And Other									$ (47,907)	$ (54,519)	$ (53,864)
Interest expense									(356,638)	(343,795)	(354,802)
Income Tax Expense (Benefit)									(17,073)	(30,092)	(255,143)
Net income (loss)									210,708	235,622	175,194
Comprehensive income (loss)									203,761	182,702	184,624
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities									527,336	904,181	972,131
Payments for (Proceeds from) Other Investing Activities									(6,908)	(2,097)	195
Net Cash Provided by (Used in) Investing Activities									(952,479)	(1,070,573)	(1,040,330)
Payments of Dividends									64,220	77,204	123,307
Proceeds from Issuance of Long-term Debt									689,351	804,050	90,120
Repayments of Long-term Debt									0	600,000	0
Net Cash Provided by (Used in) Financing Activities									435,727	185,193	63,664
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect									10,584	18,801	(4,535)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 66,146				$ 55,562				66,146	55,562	36,761	$ 41,296
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Nonutility Expense And Other									(1,495)	(1,345)	(1,466)
Equity In Net Income (Loss) Of Subsidiaries									294,724	320,122	323,568
Non-hedged interest rate derivative expense									0	0	28
Investment Income, Interest									6,643	4,273	1,039
Interest expense									(111,716)	(108,816)	(106,072)
Income Tax Expense (Benefit)									22,552	21,388	(41,903)
Net income (loss)	150,949	$ (39,443)	$ (32,952)	$ 132,154	107,053	$ (21,970)	$ 3,642	$ 146,897	210,708	235,622	175,194
Comprehensive income (loss)									203,761	182,702	184,624
Condensed Cash Flow Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities									68,724	79,176	139,005
Adjustments to Additional Paid in Capital, Other									210,000	0	24,222
Payments for (Proceeds from) Loans Receivable from Subsidiary									41,708	59,864	78,155
Payments for (Proceeds from) Other Investing Activities									0	0	437
Net Cash Provided by (Used in) Investing Activities									(251,708)	(59,864)	(102,814)
Payments of Dividends									64,220	77,204	123,307
Proceeds from Issuance of Long-term Debt									246,200	209,300	0
Repayments of Long-term Debt									0	150,000	(90,120)
Issue costs and others									116	92	2,650
Net Cash Provided by (Used in) Financing Activities									181,864	(17,996)	(35,837)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect									(1,120)	1,316	354
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 947				$ 2,067				$ 947	$ 2,067	$ 751	$ 397