Fair Value Measurements Assets and Liabilities Measured on Recurring Basis (Details) (USD $)	3 Months Ended				6 Months Ended
	Jun. 30, 2013 power_purchase_contract		Jun. 30, 2012		Jun. 30, 2013 power_purchase_contract		Jun. 30, 2012		Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Measurements, Sensitivity Analysis, Hypothetical Increase or Decrease of Market Prices, Result on Fair Value	$ 24,100,000				$ 24,100,000
Finite-lived Intangible Assets, Fair Value Disclosure	484,100,000				484,100,000
Number of Purchased Power Contracts Impaired	1				1
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings	12,799,000	[1]	(5,077,000)	[1]	11,201,000	[1]	16,870,000	[1]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Regulatory Assets (Liabilities)	(684,000)		(4,000)		(10,000)		(1,287,000)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	2,183,000	[2]	14,696,000	[2]	7,834,000	[2]	35,520,000	[2]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers Into Level 3	830,000		38,971,000		8,530,000		55,845,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3	334,000		46,461,000		7,661,000		50,562,000
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	39,772,000		83,272,000		39,772,000		83,272,000		27,976,000	35,526,000	110,531,000	95,352,000
Electric portfolio [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	(15,600,000)		6,200,000		(14,200,000)		(12,800,000)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings	12,799,000	[1]	(5,077,000)	[1]	11,201,000	[1]	16,870,000	[1]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Regulatory Assets (Liabilities)	0		0		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	2,678,000	[2]	14,372,000	[2]	9,062,000	[2]	35,415,000	[2]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers Into Level 3	830,000		38,674,000		8,530,000		55,548,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3	494,000		46,136,000		7,694,000		46,861,000
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	36,899,000		80,453,000		36,899,000		80,453,000		26,442,000	33,924,000	107,364,000	90,311,000
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]	0	[1]	0	[1]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Regulatory Assets (Liabilities)	(684,000)		(4,000)		(10,000)		(1,287,000)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	(495,000)	[2]	324,000	[2]	(1,228,000)	[2]	105,000	[2]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers Into Level 3	0		297,000		0		297,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3	(160,000)		325,000		(33,000)		3,701,000
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	2,873,000		2,819,000		2,873,000		2,819,000		1,534,000	1,602,000	3,167,000	5,041,000
Commodity Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets	16,891,000				16,891,000					21,683,000
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	13,706,000				13,706,000					21,524,000
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	13,706,000				13,706,000					21,524,000
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					0
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					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	13,706,000				13,706,000					21,524,000
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	13,706,000				13,706,000					21,524,000
Fair Value, Measurements, Recurring [Member] | Subsidiaries [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets	6,329,000				6,329,000					8,028,000
Derivative Liabilities	110,391,000				110,391,000					190,090,000
Fair Value, Measurements, Recurring [Member] | Subsidiaries [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	3,621,000				3,621,000					1,259,000
Derivative Liabilities	40,205,000				40,205,000					88,971,000
Fair Value, Measurements, Recurring [Member] | Subsidiaries [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	2,708,000				2,708,000					6,769,000
Derivative Liabilities	70,186,000				70,186,000					101,119,000
Fair Value, Measurements, Recurring [Member] | Subsidiaries [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets	10,561,000				10,561,000					13,655,000
Derivative Liabilities	50,333,000				50,333,000					49,181,000
Fair Value, Measurements, Recurring [Member] | Subsidiaries [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	6,853,000				6,853,000					8,298,000
Derivative Liabilities	43,752,000				43,752,000					42,221,000
Fair Value, Measurements, Recurring [Member] | Subsidiaries [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	3,708,000				3,708,000					5,357,000
Derivative Liabilities	6,581,000				6,581,000					6,960,000
Fair Value, Measurements, Recurring [Member] | Subsidiaries [Member] | Total [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets	16,890,000				16,890,000					21,683,000
Derivative Liabilities	160,724,000				160,724,000					239,271,000
Fair Value, Measurements, Recurring [Member] | Subsidiaries [Member] | Total [Member] | Commodity Contract [Member] | Electric portfolio [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative Assets	10,474,000				10,474,000					9,557,000
Derivative Liabilities	83,957,000				83,957,000					131,192,000
Fair Value, Measurements, Recurring [Member] | Subsidiaries [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	6,416,000				6,416,000					12,126,000
Derivative Liabilities	76,767,000				76,767,000					108,079,000
Priest Rapids Development [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of Intangible Assets, Finite-lived	13,500,000
Finite-lived Intangible Assets, Fair Value Disclosure	33,600,000				33,600,000
Finite-Lived Intangible Assets, Net	$ 47,100,000				$ 47,100,000

[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 $(15.6) million and $6.2 million for the three months ended June 30, 2013 and 2012, respectively. 2 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 $(14.2) million and $(12.8) million for the six months ended June 30, 2013 and 2012, respectively.3

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