Retirement Benefits - Change in Net Benefit Obligation and Fair Value (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Qualified Pension Benefits
Change in benefit obligation:
Benefit obligation at beginning of period	$ 565,997		$ 532,615
Service cost	16,926		15,822		16,089
Interest cost	25,986		26,263		27,975
Amendment	0		0
Actuarial loss	40,914		18,485
Benefits paid	(33,533)		(27,188)
Medicare part D subsidy received			0
Curtailment loss/(gain)	0		0
Benefit obligation at end of period	616,290		565,997		532,615
Change in plan assets:
Fair value of plan assets at beginning of period	479,786		526,469
Actual return on plan assets	62,130		(24,495)
Employer contribution	22,800		5,000
Benefits paid	(33,533)		(27,188)
Fair value of plan assets at end of period	531,183		479,786		526,469
Funded status at end of period	(85,107)		(86,211)
SERP Pension Benefits
Change in benefit obligation:
Benefit obligation at beginning of period	48,370		44,322
Service cost	1,073		1,241
Interest cost	2,152		2,192
Amendment	(122)		0
Actuarial loss	5,483		4,467
Benefits paid	(5,161)		(2,687)
Medicare part D subsidy received	0		0
Curtailment loss/(gain)	0	[1]	(1,165)	[1]
Benefit obligation at end of period	51,795		48,370
Change in plan assets:
Fair value of plan assets at beginning of period	0		0
Actual return on plan assets	0		0
Employer contribution	5,161		2,687
Benefits paid	(5,161)		(2,687)
Fair value of plan assets at end of period	0		0
Funded status at end of period	(51,795)		(48,370)
Other Benefits
Change in benefit obligation:
Benefit obligation at beginning of period	16,436		16,579
Service cost	139		113		106
Interest cost	751		806		880
Amendment	0		0
Actuarial loss	1,199		384
Benefits paid	(1,523)		(1,855)
Medicare part D subsidy received	670		409
Curtailment loss/(gain)	0		0
Benefit obligation at end of period	17,672		16,436		16,579
Change in plan assets:
Fair value of plan assets at beginning of period	7,206		8,288
Actual return on plan assets	1,100		(170)
Employer contribution	758		943
Benefits paid	(1,523)		(1,855)
Fair value of plan assets at end of period	7,541		7,206		8,288
Funded status at end of period	(10,131)		(9,230)
PUGET SOUND ENERGY, INC. | Qualified Pension Benefits
Change in benefit obligation:
Service cost	16,926		15,822		16,089
Interest cost	$ 25,986		$ 26,263		$ 27,975

[1] A curtailment gain was recognized in OCI due to the plan amendment that ceased SERP benefits for non-officers still in the plan as of December 31, 2011.