Fair Value Measurements Assets and Liabilities Measured on Recurring Basis (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012		Dec. 31, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings	$ (1,598)	[1]	$ 21,947	[1]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Regulatory Assets (Liabilities)	674		(1,283)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	5,651	[2]	20,824	[2]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers Into Level 3	7,700		16,874
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3	7,327		4,101
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	27,976		110,531		35,526	95,352
Electric portfolio [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings	(1,598)	[1]	21,947	[1]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Regulatory Assets (Liabilities)	0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	6,384	[2]	21,042	[2]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers Into Level 3	7,700		16,874
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3	7,200		726
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	26,442		107,364		33,924	90,311
Natural gas portfolio [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings	0	[1]	0	[1]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Regulatory Assets (Liabilities)	674		(1,283)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	(733)	[2]	(218)	[2]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers Into Level 3	0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3	127		3,375
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	1,534		3,167		1,602	5,041
Commodity Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets	34,862				21,683
Fair Value, Measurements, Recurring [Member] | PUGET ENERGY [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liabilities	19,966					21,524
Fair Value, Measurements, Recurring [Member] | PUGET ENERGY [Member] | Level 2 [Member] | Interest Rate Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liabilities	19,966					21,524
Fair Value, Measurements, Recurring [Member] | PUGET ENERGY [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liabilities	0					0
Fair Value, Measurements, Recurring [Member] | PUGET ENERGY [Member] | Level 3 [Member] | Commodity Contract [Member] | Electric portfolio [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets	8,632
Derivative Liabilities	35,074
Fair Value, Measurements, Recurring [Member] | PUGET ENERGY [Member] | Level 3 [Member] | Commodity Contract [Member] | Natural gas portfolio [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets	4,893
Derivative Liabilities	6,427
Fair Value, Measurements, Recurring [Member] | PUGET ENERGY [Member] | Level 3 [Member] | Interest Rate Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liabilities	0					0
Fair Value, Measurements, Recurring [Member] | PUGET ENERGY [Member] | Total [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liabilities	19,966					21,524
Fair Value, Measurements, Recurring [Member] | PUGET ENERGY [Member] | Total [Member] | Interest Rate Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Liabilities	19,966					21,524
Fair Value, Measurements, Recurring [Member] | PUGET SOUND ENERGY, INC. [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets	21,337					8,028
Derivative Liabilities	71,718					190,090
Fair Value, Measurements, Recurring [Member] | PUGET SOUND ENERGY, INC. [Member] | Level 2 [Member] | Commodity Contract [Member] | Electric portfolio [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets	7,500					1,259
Derivative Liabilities	27,166					88,971
Fair Value, Measurements, Recurring [Member] | PUGET SOUND ENERGY, INC. [Member] | Level 2 [Member] | Commodity Contract [Member] | Natural gas portfolio [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets	13,837					6,769
Derivative Liabilities	44,552					101,119
Fair Value, Measurements, Recurring [Member] | PUGET SOUND ENERGY, INC. [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets	13,525					13,655
Derivative Liabilities	41,501					49,181
Fair Value, Measurements, Recurring [Member] | PUGET SOUND ENERGY, INC. [Member] | Level 3 [Member] | Commodity Contract [Member] | Electric portfolio [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets						8,298
Derivative Liabilities						42,221
Fair Value, Measurements, Recurring [Member] | PUGET SOUND ENERGY, INC. [Member] | Level 3 [Member] | Commodity Contract [Member] | Natural gas portfolio [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets						5,357
Derivative Liabilities						6,960
Fair Value, Measurements, Recurring [Member] | PUGET SOUND ENERGY, INC. [Member] | Total [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets	34,862					21,683
Derivative Liabilities	113,219					239,271
Fair Value, Measurements, Recurring [Member] | PUGET SOUND ENERGY, INC. [Member] | Total [Member] | Commodity Contract [Member] | Electric portfolio [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets	16,132					9,557
Derivative Liabilities	62,240					131,192
Fair Value, Measurements, Recurring [Member] | PUGET SOUND ENERGY, INC. [Member] | Total [Member] | Commodity Contract [Member] | Natural gas portfolio [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets	18,730					12,126
Derivative Liabilities	$ 50,979					$ 108,079

[1] Income Statement location: Unrealized (gain) loss on derivative instruments, net. Includes unrealized gains (losses) on derivatives still held in position as of the reporting date for electric derivatives of $1.4 million and $(19.0) million for the three months ended March 31, 2013 and 2012, respectively.

[2] The Company had no purchases, sales or issuances during the reported periods.