Accounting for Derivative Instruments and Hedging Activities Net Amount of Derivatives Reported in the Statement of Financial Position (Details) $ in Thousands, MMBTU in Millions		Sep. 30, 2017 USD ($) MMBTU	Dec. 31, 2016 USD ($) MMBTU
Liabilities:
Derivative Asset, Current		$ 16,605	$ 54,341
Derivative Liability, Current		49,820	44,310
Derivative Asset, Noncurrent		2,877	8,738
Derivative Liability, Noncurrent		15,578	16,261
Commodity Contract [Member]
Assets:
Gross Amount Recognized in the Statement of Financial Position	[1]	19,482	63,079
Gross Amounts Offset in the Statement of Financial Position		0	0
Net of Amounts Presented in the Statement of Financial Position		19,482	63,079
Commodity Contracts		(12,961)	(42,858)
Cash Collateral Received		0	0
Net Amount		6,521	20,221
Liabilities:
Gross Amount Recognized in the Statement of Financial Position	[1]	65,398	60,430
Gross Amounts Offset in the Statement of Financial Position		0	0
Net of Amounts Presented in the Statement of Financial Position		65,398	60,430
Commodity Contracts		(12,961)	(42,858)
Cash Collateral Posted		(739)	0
Net Amount		51,698	17,572
Interest Rate Contract [Member]
Liabilities:
Gross Amount Recognized in the Statement of Financial Position	[1],[2]		141
Gross Amounts Offset in the Statement of Financial Position	[2]		0
Net of Amounts Presented in the Statement of Financial Position			141
Commodity Contracts	[2]		0
Cash Collateral Posted	[2]		0
Net Amount			141
Subsidiaries [Member]
Liabilities:
Derivative Asset, Current		16,605	54,341
Derivative Liability, Current		49,820	44,170
Derivative Asset, Noncurrent		2,877	8,738
Derivative Liability, Noncurrent		15,578	16,261
Not Designated as Hedging Instrument [Member]
Assets:
Net of Amounts Presented in the Statement of Financial Position		19,482	63,079
Liabilities:
Net of Amounts Presented in the Statement of Financial Position		65,398	60,571
Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount		0	450,000
Assets:
Net of Amounts Presented in the Statement of Financial Position		0	0
Liabilities:
Net of Amounts Presented in the Statement of Financial Position		0	141
Not Designated as Hedging Instrument [Member] | Electric Portfolio [Member]
Assets:
Net of Amounts Presented in the Statement of Financial Position		11,656	36,460
Liabilities:
Net of Amounts Presented in the Statement of Financial Position		$ 39,622	$ 41,329
Not Designated as Hedging Instrument [Member] | Natural Gas Derivatives [Member]
Liabilities:
Derivative, Nonmonetary Notional Amount | MMBTU		305.3	336.4
Not Designated as Hedging Instrument [Member] | Natural Gas Portfolio [Member]
Assets:
Net of Amounts Presented in the Statement of Financial Position		$ 7,826	$ 26,619
Liabilities:
Net of Amounts Presented in the Statement of Financial Position		25,776	19,101
Not Designated as Hedging Instrument [Member] | Parent Company [Member]
Liabilities:
Derivative Asset, Current		16,605	54,341
Derivative Liability, Current		49,820	44,310
Derivative Asset, Noncurrent		2,877	8,738
Derivative Liability, Noncurrent		$ 15,578	$ 16,261

[1] 1 All derivative contract deals are executed under ISDA, NAESB and WSPP master netting agreements with right of set-off.

[2] 2 Interest rate swap contracts are only held at Puget Energy