CONSOLIDATED BALANCE SHEETS (USD $)	Dec. 31, 2012	Dec. 31, 2011
Utility Plant [Abstract]
Electric plant	$ 6,750,400,000	$ 6,090,851,000
Gas plant	2,385,784,000	2,238,741,000
Common plant	487,931,000	418,236,000
Less: Accumulated depreciation and amortization	(1,067,424,000)	(674,783,000)
Net utility plant	8,556,691,000	8,073,045,000
Other property and investments:
Goodwill	1,656,513,000	1,656,513,000
Other property and investments	112,367,000	123,352,000
Total other property and investments	1,768,880,000	1,779,865,000
Current assets:
Cash and cash equivalents	135,542,000	37,235,000
Restricted cash	3,700,000	4,183,000
Accounts receivable, net of allowance for doubtful accounts	287,784,000	336,530,000
Unbilled revenue	204,359,000	191,150,000
Materials and supplies, at average cost	82,353,000	76,068,000
Fuel and gas inventory, at average cost	88,953,000	100,491,000
Unrealized gain on derivative instruments	6,869,000	6,647,000
Income taxes	4,796,000	10,970,000
Prepaid expense and other	13,571,000	13,969,000
Power contract acquisition adjustment gain	50,785,000	65,096,000
Deferred income taxes	53,437,000	101,934,000
Total current assets	932,149,000	944,273,000
Other long-term and regulatory assets:
Regulatory asset for deferred income taxes	119,844,000	62,305,000
Power cost adjustment mechanism	3,773,000	6,818,000
Regulatory assets related to power contracts	37,655,000	46,202,000
Other regulatory assets	815,785,000	783,580,000
Unrealized gain on derivative instruments	14,814,000	10,084,000
Power contract acquisition adjustment gain	456,225,000	517,740,000
Other	95,763,000	183,394,000
Total other long-term and regulatory assets	1,543,859,000	1,610,123,000
Total assets	12,801,579,000	12,407,306,000
Common shareholder’s equity:
Common stock	0	0
Additional paid-in capital	3,308,957,000	3,308,957,000
Earnings reinvested in the business	208,100,000	22,873,000
Accumulated other comprehensive income (loss), net of tax	(32,829,000)	(30,907,000)
Total common shareholder’s equity	3,484,228,000	3,300,923,000
Long-term debt:
First mortgage bonds and senior notes	3,351,412,000	3,362,000,000
Pollution control bonds	161,860,000	161,860,000
Junior subordinated notes	250,000,000	250,000,000
Long-term debt	1,834,000,000	1,793,000,000
Debt discount and other	(264,072,000)	(289,493,000)
Total long-term debt	5,333,200,000	5,277,367,000
Total capitalization	8,817,428,000	8,578,290,000
Current liabilities:
Accounts payable	288,059,000	339,361,000
Short-term debt	181,000,000	25,000,000
Current maturities of long-term debt	13,000,000	0
Purchased gas adjustment liability	32,587,000	25,940,000
Accrued expenses:
Taxes	95,623,000	90,727,000
Salaries and wages	38,438,000	40,892,000
Interest	82,262,000	69,329,000
Unrealized loss on derivative instruments	177,519,000	327,089,000
Power contract acquisition adjustment loss	3,902,000	8,547,000
Other	72,799,000	74,409,000
Total current liabilities	985,189,000	1,001,294,000
Long-term and regulatory liabilities:
Deferred income taxes	1,261,636,000	1,153,172,000
Unrealized loss on derivative instruments	83,276,000	196,558,000
Regulatory liabilities	600,697,000	369,403,000
Regulatory liabilities related to power contracts	507,009,000	582,836,000
Power contract acquisition adjustment loss	33,753,000	37,655,000
Other deferred credits	512,591,000	488,098,000
Total long-term and regulatory liabilities	2,998,962,000	2,827,722,000
Commitments and contingencies (Note 16)
Total capitalization and liabilities	12,801,579,000	12,407,306,000
PUGET SOUND ENERGY, INC.
Utility Plant [Abstract]
Electric plant	9,048,356,000	8,413,846,000
Gas plant	2,998,188,000	2,855,794,000
Common plant	555,549,000	518,318,000
Less: Accumulated depreciation and amortization	(4,045,402,000)	(3,714,913,000)
Net utility plant	8,556,691,000	8,073,045,000
Other property and investments:
Other property and investments	103,646,000	113,528,000
Total other property and investments	103,646,000	113,528,000
Current assets:
Cash and cash equivalents	135,530,000	31,010,000
Restricted cash	3,700,000	4,183,000
Accounts receivable, net of allowance for doubtful accounts	287,989,000	336,483,000
Unbilled revenue	204,359,000	191,150,000
Materials and supplies, at average cost	82,353,000	76,069,000
Fuel and gas inventory, at average cost	85,547,000	97,074,000
Unrealized gain on derivative instruments	6,869,000	6,647,000
Income taxes	4,796,000	10,970,000
Prepaid expense and other	13,414,000	13,807,000
Deferred income taxes	68,015,000	112,204,000
Total current assets	892,572,000	879,597,000
Other long-term and regulatory assets:
Regulatory asset for deferred income taxes	119,279,000	61,344,000
Power cost adjustment mechanism	3,773,000	6,818,000
Other regulatory assets	813,171,000	777,341,000
Unrealized gain on derivative instruments	14,814,000	10,084,000
Other	90,330,000	186,386,000
Total other long-term and regulatory assets	1,041,367,000	1,041,973,000
Total assets	10,594,276,000	10,108,143,000
Common shareholder’s equity:
Common stock	859,000	859,000
Additional paid-in capital	3,246,205,000	3,246,205,000
Earnings reinvested in the business	344,280,000	163,735,000
Accumulated other comprehensive income (loss), net of tax	(187,198,000)	(188,579,000)
Total common shareholder’s equity	3,404,146,000	3,222,220,000
Long-term debt:
First mortgage bonds and senior notes	3,351,412,000	3,362,000,000
Pollution control bonds	161,860,000	161,860,000
Junior subordinated notes	250,000,000	250,000,000
Debt discount and other	(14,000)	(15,000)
Total long-term debt	3,763,258,000	3,773,845,000
Total capitalization	7,167,404,000	6,996,065,000
Current liabilities:
Accounts payable	288,257,000	339,568,000
Short-term debt	181,000,000	25,000,000
Short-term note owed to parent	29,598,000	29,998,000
Current maturities of long-term debt	13,000,000	0
Purchased gas adjustment liability	32,587,000	25,940,000
Accrued expenses:
Taxes	95,623,000	90,727,000
Salaries and wages	38,438,000	40,892,000
Interest	55,806,000	55,843,000
Unrealized loss on derivative instruments	170,948,000	301,879,000
Other	69,882,000	68,346,000
Total current liabilities	975,139,000	978,193,000
Long-term and regulatory liabilities:
Deferred income taxes	1,274,602,000	1,115,056,000
Unrealized loss on derivative instruments	68,323,000	169,359,000
Regulatory liabilities	596,324,000	364,085,000
Other deferred credits	512,484,000	485,385,000
Total long-term and regulatory liabilities	2,451,733,000	2,133,885,000
Commitments and contingencies (Note 16)
Total capitalization and liabilities	$ 10,594,276,000	$ 10,108,143,000