Accounting for Derivative Instruments and Hedging Activities Recognized in Statement of Income (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Derivative Instruments, (Loss) Gain [Line Items]
Document Period End Date			Sep. 30, 2013
Purchased electricity	$ 92,774,000	$ 85,933,000	$ 380,360,000	$ 441,145,000
Unrealized (gain) loss on derivative instruments	(8,888,000)	(67,490,000)	(57,203,000)	(126,840,000)
PUGET ENERGY [Member]
Derivative Instruments, (Loss) Gain [Line Items]
Derivative Instruments, Amount Not Designated as Normal Purchase, Normal Sale				2,200,000
Subsidiaries [Member]
Derivative Instruments, (Loss) Gain [Line Items]
Document Period End Date			Sep. 30, 2013
Purchased electricity	92,774,000	85,933,000	380,360,000	441,145,000
Unrealized (gain) loss on derivative instruments	(8,888,000)	(65,594,000)	(54,252,000)	(115,309,000)
Not Designated as Hedging Instrument [Member] | PUGET ENERGY [Member]
Derivative Instruments, (Loss) Gain [Line Items]
Unrealized (gain) loss on derivative instruments	2,068,000	(12,159,000)	927,000	67,602,000
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	470,000	(1,512,000)	(1,790,000)	5,258,000
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	3,625,000	7,548,000	4,301,000	26,812,000
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	(8,888,000)	(67,442,000)	(57,203,000)	(124,641,000)
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	9,142,000	26,998,000	22,710,000	52,972,000
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	(2,281,000)	22,249,000	32,909,000	107,201,000
Not Designated as Hedging Instrument [Member] | Subsidiaries [Member]
Derivative Instruments, (Loss) Gain [Line Items]
Unrealized (gain) loss on derivative instruments	(2,027,000)	(16,347,000)	1,367,000	44,865,000
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	(8,888,000)	(65,594,000)	(54,252,000)	(115,309,000)
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	9,142,000	26,998,000	22,710,000	52,972,000
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	(2,281,000)	22,249,000	32,909,000	107,202,000
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	(1,247,000)	(2,015,000)	(3,722,000)	(16,666,000)
Cash Flow Hedging [Member] | PUGET ENERGY [Member] | Interest expense [Member]
Derivative Instruments, (Loss) Gain [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net		(1,623,000)		(16,386,000)
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	0	100,000
Cash Flow Hedging [Member] | PUGET ENERGY [Member] | Purchased electricity [Member]
Derivative Instruments, (Loss) Gain [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net		(392,000)		(380,000)
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	(122,000)	(2,362,000)	(3,152,000)	(9,977,000)
Cash Flow Hedging [Member] | Subsidiaries [Member] | Interest expense [Member]
Derivative Instruments, (Loss) Gain [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net		(122,000)		(366,000)
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	0	97,000
Cash Flow Hedging [Member] | Subsidiaries [Member] | Purchased electricity [Member]
Derivative Instruments, (Loss) Gain [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net		(2,240,000)		(9,708,000)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Cash Flow Hedging [Member] | Subsidiaries [Member] | Purchased electricity [Member]
Derivative Instruments, (Loss) Gain [Line Items]
Purchased electricity	$ 0