Summary of Significant Accounting Policies (Details) (USD $)	12 Months Ended					12 Months Ended
	Dec. 31, 2012 unit	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011	Feb. 06, 2009	Dec. 31, 2012 Electric Transmission	Dec. 31, 2010 Electric Transmission	Dec. 31, 2009 Electric Transmission	Dec. 31, 2012 Gas Transmission Equipment	Dec. 31, 2010 Gas Transmission Equipment	Dec. 31, 2009 Gas Transmission Equipment	Dec. 31, 2012 PUGET SOUND ENERGY, INC. sqmi	Dec. 31, 2011 PUGET SOUND ENERGY, INC.	Dec. 31, 2010 PUGET SOUND ENERGY, INC.	Dec. 31, 2009 PUGET SOUND ENERGY, INC.
Accounting Policies
Area of service territory (sqmi)												6,000
Annual depreciation provision	11.60%	11.30%	11.80%			2.90%	2.70%	2.70%	3.40%	3.50%	3.60%
Recognition of goodwill due to merger					$ 1,700,000,000
Number of reportable segments	1
Cash and Cash Equivalents
Cash and cash equivalents	135,542,000	36,557,000	78,527,000	37,235,000								135,530,000	31,010,000	36,320,000	78,407,000
Cash equivalents	107,600,000			16,800,000
Revenue Recognition
Excise taxes collected												244,200,000	252,500,000	231,100,000
Allowance for Doubtful Accounts
Allowance for doubtful accounts	9,932,000	8,500,000		8,495,000								9,932,000	8,495,000
Self Insurance [Abstract]
Certain Uninsured Qualifying Storm Damage Costs	8,000,000
Statements of Cash Flows
Incurred capital lease obligations												$ 33,200,000	$ 37,900,000	$ 0