Accounting for Derivative Instruments and Hedging Activities (Schedule of Effects of Non-hedging Derivative Instuments on Income) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Derivative Instruments, Gain (Loss) [Line Items]
Total gain (loss) recognized in income on derivatives	$ 133,606,000		$ (11,494,000)		$ (54,095,000)
Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Total gain (loss) recognized in income on derivatives	(107,921,000)		(262,870,000)		(230,591,000)
Not Designated as Hedging Instrument | Interest rate contracts: | Other Deductions
Derivative Instruments, Gain (Loss) [Line Items]
Total gain (loss) recognized in income on derivatives	(4,288,000)		(28,601,000)		(7,955,000)
Not Designated as Hedging Instrument | Interest rate contracts: | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Total gain (loss) recognized in income on derivatives	(29,727,000)		(46,045,000)		9,423,000
Not Designated as Hedging Instrument | Commodity contracts: | Net Unrealized Gain (Loss) on Derivative Instruments
Derivative Instruments, Gain (Loss) [Line Items]
Total gain (loss) recognized in income on derivatives	131,407,000	[1]	(23,171,000)	[1]	(94,659,000)	[1]
Amortization expense excluded from gain (loss) on derivative instruments	2,200,000		11,700,000		40,600,000
Not Designated as Hedging Instrument | Commodity contracts: | Electric Generation Fuel
Derivative Instruments, Gain (Loss) [Line Items]
Total gain (loss) recognized in income on derivatives	(66,762,000)		(98,208,000)		(100,514,000)
Not Designated as Hedging Instrument | Commodity contracts: | Purchased Electricity
Derivative Instruments, Gain (Loss) [Line Items]
Total gain (loss) recognized in income on derivatives	(138,551,000)		(66,845,000)		(36,886,000)
PUGET SOUND ENERGY, INC.
Derivative Instruments, Gain (Loss) [Line Items]
Total gain (loss) recognized in income on derivatives	119,120,000		(54,146,000)		(166,953,000)
PUGET SOUND ENERGY, INC. | Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Total gain (loss) recognized in income on derivatives	(86,193,000)		(219,199,000)		(304,353,000)
PUGET SOUND ENERGY, INC. | Not Designated as Hedging Instrument | Commodity contracts: | Net Unrealized Gain (Loss) on Derivative Instruments
Derivative Instruments, Gain (Loss) [Line Items]
Total gain (loss) recognized in income on derivatives	119,120,000		(54,146,000)		(166,953,000)
PUGET SOUND ENERGY, INC. | Not Designated as Hedging Instrument | Commodity contracts: | Electric Generation Fuel
Derivative Instruments, Gain (Loss) [Line Items]
Total gain (loss) recognized in income on derivatives	(66,762,000)		(98,208,000)		(100,514,000)
PUGET SOUND ENERGY, INC. | Not Designated as Hedging Instrument | Commodity contracts: | Purchased Electricity
Derivative Instruments, Gain (Loss) [Line Items]
Total gain (loss) recognized in income on derivatives	$ (138,551,000)		$ (66,845,000)		$ (36,886,000)

[1] Differs from the amounts stated in the statements 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 twelve months ended December 31, 2012 and $11.7 million for the twelve months ended December 31, 2011, and $40.6 million for the twelve months ended December 31, 2010.