Accumulated Other Comprehensive Income - Changes by Component (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income tax (benefit) expense	$ (957)	$ 20,000	$ 69,634	$ 52,346
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of Period			(32,829)
Other Comprehensive Income Reclassification Of Net Unrealized Gain Loss On Interest Rate Swaps During Period Net Of Tax		(7,088)	(1,715)	(9,596)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	1,107	104	760	209
Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, Net of Tax	0	122	(107)	(73)
End of Period	(31,981)		(31,981)
PUGET ENERGY [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of Period	(31,735)		(32,829)
Other comprehensive income (loss) before reclassifications	(1,548)		(1,548)
Amounts reclassified from accumulated other comprehensive income (loss), net of tax	1,302		2,396
Net current-period other comprehensive income (loss)	(246)		848
End of Period	(31,981)		(31,981)
PUGET ENERGY [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Interest Rate Contract [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of Period	(2,168)		(3,022)
Other comprehensive income (loss) before reclassifications	0		0
Other Comprehensive Income Reclassification Of Net Unrealized Gain Loss On Interest Rate Swaps During Period Net Of Tax	(861)
Net current-period other comprehensive income (loss)	861		1,715
End of Period	(1,307)		(1,307)
PUGET ENERGY [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Energy Related Derivative [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of Period	(849)		(742)
Other comprehensive income (loss) before reclassifications	0		0
Net current-period other comprehensive income (loss)	0		(107)
End of Period	(849)		(849)
PUGET ENERGY [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of Period	(28,718)		(29,065)
Other comprehensive income (loss) before reclassifications	(1,548)		(1,548)
Amounts reclassified from accumulated other comprehensive income (loss), net of tax	441		788
Net current-period other comprehensive income (loss)	(1,107)		(760)
End of Period	(29,825)		(29,825)
Subsidiaries [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income tax (benefit) expense	11,180	31,087	90,941	77,301
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of Period	(181,922)		(187,198)
Other comprehensive income (loss) before reclassifications	(1,548)		(1,548)
Amounts reclassified from accumulated other comprehensive income (loss), net of tax	3,506		8,782
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax	(1,879)	(1,227)	(5,265)	(3,643)
Other Comprehensive Income (Loss), Reclassification Adjustment on Derivatives Included in Net Income, Net of Tax	0	2,869	1,811	4,791
Amortization Of Financing Cash Flow Hedge Contracts To Earnings During Period Net Of Tax	79	79	158	159
Net current-period other comprehensive income (loss)	1,958		7,234
End of Period	(179,964)		(179,964)
Subsidiaries [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Interest Rate Contract [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of Period	(172,612)		(175,998)
Other comprehensive income (loss) before reclassifications	(1,548)		(1,548)
Amounts reclassified from accumulated other comprehensive income (loss), net of tax	3,427		6,813
End of Period	(170,733)		(170,733)
Subsidiaries [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Energy Related Derivative [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of Period	(6,545)		(6,624)
Other comprehensive income (loss) before reclassifications	0		0
Net current-period other comprehensive income (loss)	79
End of Period	(6,466)		(6,466)
Subsidiaries [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning of Period	(2,765)		(4,576)
Other comprehensive income (loss) before reclassifications	0		0
Amounts reclassified from accumulated other comprehensive income (loss), net of tax	0
End of Period	(2,765)		(2,765)
Reclassification out of Accumulated Other Comprehensive Income [Member] | PUGET ENERGY [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Interest Rate Contract [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income tax (benefit) expense	(464)		(924)
Reclassification out of Accumulated Other Comprehensive Income [Member] | PUGET ENERGY [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Energy Related Derivative [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income tax (benefit) expense	0		57
Reclassification out of Accumulated Other Comprehensive Income [Member] | PUGET ENERGY [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income tax (benefit) expense	(237)		(422)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Subsidiaries [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Interest Rate Contract [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income tax (benefit) expense	(43)		(86)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Subsidiaries [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member] | Energy Related Derivative [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income tax (benefit) expense	0		(975)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Subsidiaries [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income tax (benefit) expense	$ (1,845)		$ (3,666)