Accumulated Other Comprehensive Income - Reclassification Location (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Interest expense	$ (94,788)	$ (96,507)	$ (299,521)	$ (299,672)
Purchased electricity	92,774	85,933	380,360	441,145
Income (loss) before income taxes	14,476	67,635	252,488	266,152
Net income (loss)	8,540	46,692	176,919	192,863
Income Tax Expense (Benefit)	(5,936)	(20,943)	(75,569)	(73,289)
PUGET ENERGY [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Net income (loss)	(1,204)		(3,600)
PUGET ENERGY [Member] | Accumulated Defined Benefit Plans Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Amortization of prior service cost	499		1,498
Amortization of net gain (loss)	(1,104)		(3,315)
Income (loss) before income taxes	(605)		(1,817)
Net income (loss)	(393)		(1,181)
Income Tax Expense (Benefit)	212		636
PUGET ENERGY [Member] | Interest Rate Contract [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Interest expense	1,247		3,886
Net income (loss)	(811)		(2,526)
Income Tax Expense (Benefit)	(436)		(1,360)
PUGET ENERGY [Member] | Energy Related Derivative [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Purchased electricity	0		164
Net income (loss)	0		107
Income Tax Expense (Benefit)	0		57
Subsidiaries [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Interest expense	(64,614)	(61,524)	(196,363)	(184,595)
Purchased electricity	92,774	85,933	380,360	441,145
Income (loss) before income taxes	41,135	97,817	338,675	368,706
Net income (loss)	26,605	66,868	233,205	260,456
Income Tax Expense (Benefit)	(14,530)	(30,949)	(105,470)	(108,250)
Subsidiaries [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Net income (loss)	(3,485)		(12,266)
Subsidiaries [Member] | Accumulated Defined Benefit Plans Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Amortization of prior service cost	390		1,171
Amortization of net gain (loss)	(5,630)		(16,891)
Income (loss) before income taxes	(5,240)		(15,720)
Net income (loss)	(3,406)		(10,219)
Income Tax Expense (Benefit)	1,834		5,501
Subsidiaries [Member] | Interest Rate Contract [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Interest expense	122		366
Net income (loss)	(79)		(237)
Income Tax Expense (Benefit)	(43)		129
Subsidiaries [Member] | Energy Related Derivative [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification out of Accumulated Other Comprehensive Income [Line Items]
Purchased electricity	0		(2,786)
Net income (loss)			(1,810)
Income Tax Expense (Benefit)	$ 0		$ (976)