Liquidity Facilities and Other Financing Arrangements (Details) - USD ($) $ in Thousands				12 Months Ended
	Aug. 31, 2023	Sep. 26, 2022	Feb. 10, 2012	Dec. 31, 2023	Dec. 31, 2022	May 16, 2022
Short-term Debt [Line Items]
Short-term debt				$ 598,100	$ 441,300
Line of Credit Facility, Maximum Borrowing Capacity				1,300,000
Proceeds from Lines of Credit	$ 100,000	$ 50,000
Line of Credit, Current				261,500	84,300
Long-term Line of Credit, Noncurrent				0	34,300
Working Capital Needs
Short-term Debt [Line Items]
Current borrowing capacity of line of credit						$ 800,000
Subsidiaries [Member]
Short-term Debt [Line Items]
Short-term debt				$ 336,600	$ 357,000
Weighted-average interest rate on short-term debt (percent)				9.00%	6.10%
Line of Credit Facility, Current Same-Day Borrowing Capacity				$ 75,000
Line of Credit Facility, Maximum Borrowing Capacity				$ 1,400,000
Maximum capitalization percentage				65.00%
Derivative, Basis Spread on Variable Rate				1.25%
Line of Credit, Unused Capacity, Commitment Fee Percentage				0.175%
Promissory Note Outstanding, Amount				$ 0
Subsidiaries [Member] | Standby Letters of Credit
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				150,000
Subsidiaries [Member] | Working Capital Needs
Short-term Debt [Line Items]
Current borrowing capacity of line of credit						$ 800,000
Subsidiaries [Member] | Letter of Credit | Working Capital Needs
Short-term Debt [Line Items]
Current borrowing capacity of line of credit				2,100
Subsidiaries [Member] | Letter of Credit | Energy Dedging Activities
Short-term Debt [Line Items]
Current borrowing capacity of line of credit				51,000
Subsidiaries [Member] | Line of Credit [Member] | Promissory Note with Puget Energy
Short-term Debt [Line Items]
Current borrowing capacity of line of credit				200,000
Parent
Short-term Debt [Line Items]
Short-term debt				$ 261,500	$ 84,300
Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Basis spread on variable rate (percent)				1.75%
Line of Credit Facility, Commitment Fee Percentage			0.275%
Line of Credit Facility, Fair Value of Amount Outstanding					$ 118,600
Debt Instrument, Secured Overnight Financing Rate Adjustment				0.10%
Revolving Credit Facility [Member] | Subsidiaries [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Fair Value of Amount Outstanding				$ 0
Debt Instrument, Secured Overnight Financing Rate Adjustment				0.10%