Income Taxes - Income Tax Reconciliation (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Tax Disclosures [Line Items]
Federal statutory rate	35.00%
Income Tax Reconciliation [Abstract]
Income taxes at the statutory rate	$ 132,491	$ 54,968	$ 11,477
Production tax credit	(22,188)	(23,310)	(19,972)
AFUDC excluded from taxable income	(16,543)	(22,861)	(9,970)
Capitalized interest	9,757	17,592	8,244
Utility plant differences	8,674	5,849	6,162
Tenaska gas contract	(4,687)	7,094	5,889
Other - net	(2,779)	(5,572)	651
Total income tax expense	104,725	33,760	2,481
Effective tax rate	27.70%	21.50%	7.60%
PUGET SOUND ENERGY, INC.
Income Tax Reconciliation [Abstract]
Income taxes at the statutory rate	176,917	98,783	9,176
Production tax credit	(22,188)	(23,310)	(19,972)
AFUDC excluded from taxable income	(16,543)	(22,861)	(9,970)
Capitalized interest	9,757	17,592	8,244
Utility plant differences	8,674	5,849	6,162
Tenaska gas contract	(4,687)	7,094	5,889
Other - net	(2,622)	(5,030)	593
Total income tax expense	$ 149,308	$ 78,117	$ 122
Effective tax rate	29.50%	27.70%	0.50%