Accounting for Derivative Instruments and Hedging Activities Recognized in Statement of Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Derivative Instruments, (Loss) Gain [Line Items]
Document Period End Date	Mar. 31, 2014
Purchased electricity	$ 181,157	$ 175,043
Unrealized (gain) loss on derivative instruments	(7,839)	(75,692)
Subsidiaries [Member]
Derivative Instruments, (Loss) Gain [Line Items]
Document Period End Date	Mar. 31, 2014
Purchased electricity	181,157	175,043
Unrealized (gain) loss on derivative instruments	(7,270)	(72,740)
Not Designated as Hedging Instrument [Member] | PUGET ENERGY [Member]
Derivative Instruments, (Loss) Gain [Line Items]
Unrealized (gain) loss on derivative instruments	(20,177)	(30,019)
Not Designated as Hedging Instrument [Member] | PUGET ENERGY [Member] | Other Income (Deductions) [Member] | Interest Expense [Member]
Derivative Instruments, (Loss) Gain [Line Items]
Unrealized (gain) loss on derivative instruments	747	(1,028)
Not Designated as Hedging Instrument [Member] | PUGET ENERGY [Member] | Interest Rate Contract [Member] | Interest Expense [Member]
Derivative Instruments, (Loss) Gain [Line Items]
Unrealized (gain) loss on derivative instruments	125	2,578
Not Designated as Hedging Instrument [Member] | PUGET ENERGY [Member] | Commodity Contract [Member] | Unrealized (Gain) Loss on Derivative Instruments, Net [Member]
Derivative Instruments, (Loss) Gain [Line Items]
Unrealized (gain) loss on derivative instruments	(7,839)	(75,692)
Not Designated as Hedging Instrument [Member] | PUGET ENERGY [Member] | Commodity Contract [Member] | Electric generation fuel [Member]
Derivative Instruments, (Loss) Gain [Line Items]
Unrealized (gain) loss on derivative instruments	(7,827)	12,638
Not Designated as Hedging Instrument [Member] | PUGET ENERGY [Member] | Commodity Contract [Member] | Purchased Electricity [Member]
Derivative Instruments, (Loss) Gain [Line Items]
Unrealized (gain) loss on derivative instruments	(5,383)	31,485
Not Designated as Hedging Instrument [Member] | Subsidiaries [Member]
Derivative Instruments, (Loss) Gain [Line Items]
Unrealized (gain) loss on derivative instruments	(20,480)	(28,617)
Not Designated as Hedging Instrument [Member] | Subsidiaries [Member] | Commodity Contract [Member] | Unrealized (Gain) Loss on Derivative Instruments, Net [Member]
Derivative Instruments, (Loss) Gain [Line Items]
Unrealized (gain) loss on derivative instruments	(7,270)	(72,740)
Not Designated as Hedging Instrument [Member] | Subsidiaries [Member] | Commodity Contract [Member] | Electric generation fuel [Member]
Derivative Instruments, (Loss) Gain [Line Items]
Unrealized (gain) loss on derivative instruments	(7,827)	12,638
Not Designated as Hedging Instrument [Member] | Subsidiaries [Member] | Commodity Contract [Member] | Purchased Electricity [Member]
Derivative Instruments, (Loss) Gain [Line Items]
Unrealized (gain) loss on derivative instruments	(5,383)	31,485
Cash Flow Hedging [Member] | PUGET ENERGY [Member]
Derivative Instruments, (Loss) Gain [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(678)	(1,150)
Cash Flow Hedging [Member] | PUGET ENERGY [Member] | Electric generation fuel [Member]
Derivative Instruments, (Loss) Gain [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	0	0
Cash Flow Hedging [Member] | Subsidiaries [Member]
Derivative Instruments, (Loss) Gain [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(1,226)	(2,908)
Cash Flow Hedging [Member] | Subsidiaries [Member] | Electric generation fuel [Member]
Derivative Instruments, (Loss) Gain [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	$ 0	$ 0