Accounting for Derivative Instruments and Hedging Activities (Schedule of Amounts Recognized in Statement of Income) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Derivative Instruments, (Loss) Gain [Line Items]
Unrealized (gain) loss on derivative instruments	$ 84,146		$ (102,744)		$ (133,606)
PUGET SOUND ENERGY, INC.
Derivative Instruments, (Loss) Gain [Line Items]
Unrealized (gain) loss on derivative instruments	85,636		(98,880)		(119,120)
Not Designated as Hedging Instrument | Interest Rate Contract | Other Income (Deductions)
Derivative Instruments, (Loss) Gain [Line Items]
Unrealized (gain) loss on derivative instruments	3,915		(2,420)		4,288
Not Designated as Hedging Instrument | Interest Rate Contract | Interest Expense
Derivative Instruments, (Loss) Gain [Line Items]
Unrealized (gain) loss on derivative instruments	(500)		5,904		29,727
Not Designated as Hedging Instrument | Commodity Contract | Unrealized (Gain) Loss on Derivative Instruments, Net
Derivative Instruments, (Loss) Gain [Line Items]
Unrealized (gain) loss on derivative instruments	84,146	[1]	(102,744)	[1]	(131,407)	[1]
Not Designated as Hedging Instrument | Commodity Contract | Electric Generation Fuel
Derivative Instruments, (Loss) Gain [Line Items]
Unrealized (gain) loss on derivative instruments	(6,511)		27,008		66,762
Not Designated as Hedging Instrument | Commodity Contract | Purchased Electricity
Derivative Instruments, (Loss) Gain [Line Items]
Unrealized (gain) loss on derivative instruments	4,212		38,299		138,551
Not Designated as Hedging Instrument | PUGET ENERGY
Derivative Instruments, (Loss) Gain [Line Items]
Unrealized (gain) loss on derivative instruments	85,262		(33,953)		107,921
Not Designated as Hedging Instrument | PUGET SOUND ENERGY, INC.
Derivative Instruments, (Loss) Gain [Line Items]
Unrealized (gain) loss on derivative instruments	83,337		(33,573)		86,193
Not Designated as Hedging Instrument | PUGET SOUND ENERGY, INC. | Commodity Contract | Unrealized (Gain) Loss on Derivative Instruments, Net
Derivative Instruments, (Loss) Gain [Line Items]
Unrealized (gain) loss on derivative instruments	85,636		(98,880)		(119,120)
Not Designated as Hedging Instrument | PUGET SOUND ENERGY, INC. | Commodity Contract | Electric Generation Fuel
Derivative Instruments, (Loss) Gain [Line Items]
Unrealized (gain) loss on derivative instruments	(6,511)		27,008		66,762
Not Designated as Hedging Instrument | PUGET SOUND ENERGY, INC. | Commodity Contract | Purchased Electricity
Derivative Instruments, (Loss) Gain [Line Items]
Unrealized (gain) loss on derivative instruments	$ 4,212		$ 38,299		$ 138,551

[1] For 2012, the amount differs from the amount stated in the statement of income as it does not include amortization related to contracts that were recorded at fair value at the time of the February 2009 merger and subsequently designated as NPNS of $2.2 million for the year ended December 31, 2012.