SCHEDULE I CONDENSED FINANCIAL INFORMATION OF PUGET ENERGY - Condensed Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Property And Investments [Abstract]
Goodwill	$ 1,656,513	$ 1,656,513
Current assets:
Cash and Cash Equivalents, at Carrying Value	45,259	37,521
Total current assets	835,119	857,376
Assets, Noncurrent [Abstract]
Other	92,980	77,523
Total assets	14,659,863	14,098,861
Capitalization, Long-term Debt and Equity [Abstract]
Stockholders' Equity Attributable to Parent	4,000,299	3,860,758	$ 3,750,030	$ 3,688,713
Long-term debt	1,758,100	1,961,900
Total capitalization	9,920,624	9,533,249
Current liabilities:
Accounts payable	325,913	480,069
Interest	74,855	70,099
Deferred income taxes	824,720	789,297
Unrealized loss on derivative instruments	13,428	46,661
Total current liabilities	1,318,767	1,226,882
Liabilities, Noncurrent [Abstract]
Unrealized loss on derivative instruments	12,693	11,095
Total capitalization and liabilities	14,659,863	14,098,861
Current maturities of long-term debt	452,412	0
Parent Company [Member]
Assets
Investments in subsidiaries	4,153,618	3,820,347
Other Property And Investments [Abstract]
Goodwill	1,656,513	1,656,513
Current assets:
Cash and Cash Equivalents, at Carrying Value	947	2,067
Receivables from affiliates	180,527	138,714
Total current assets	181,474	140,781
Assets, Noncurrent [Abstract]
Deferred Tax Assets, Net of Valuation Allowance, Noncurrent	235,428	221,660
Other	2,056	2,040
Assets, Noncurrent, Total	237,484	223,700
Total assets	6,229,089	5,841,341
Capitalization, Long-term Debt and Equity [Abstract]
Stockholders' Equity Attributable to Parent	4,000,299	3,860,728
Long-term debt	1,752,644	1,954,205
Total capitalization	5,752,943	5,814,933
Current liabilities:
Accounts payable	208	260
Interest	25,938	26,148
Total current liabilities	476,146	26,408
Liabilities, Noncurrent [Abstract]
Total capitalization and liabilities	6,229,089	5,841,341
Current maturities of long-term debt	$ 450,000	$ 0