Retirement Benefits Net Periodic Benefit Cost (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended
	Mar. 31, 2013 Qualified Pension Benefits [Member]	Dec. 31, 2011 Qualified Pension Benefits [Member]	Mar. 31, 2013 SERP Pension Benefits [Member]	Dec. 31, 2011 SERP Pension Benefits [Member]	Mar. 31, 2013 Other Benefit [Member]	Dec. 31, 2011 Other Benefit [Member]	Mar. 31, 2013 PUGET ENERGY [Member] Qualified Pension Benefits [Member]	Mar. 31, 2012 PUGET ENERGY [Member] Qualified Pension Benefits [Member]	Mar. 31, 2013 PUGET ENERGY [Member] SERP Pension Benefits [Member]	Mar. 31, 2012 PUGET ENERGY [Member] SERP Pension Benefits [Member]	Mar. 31, 2013 PUGET ENERGY [Member] Other Benefit [Member]	Mar. 31, 2012 PUGET ENERGY [Member] Other Benefit [Member]	Mar. 31, 2013 PUGET SOUND ENERGY, INC. [Member] Qualified Pension Benefits [Member]	Mar. 31, 2012 PUGET SOUND ENERGY, INC. [Member] Qualified Pension Benefits [Member]	Mar. 31, 2013 PUGET SOUND ENERGY, INC. [Member] SERP Pension Benefits [Member]	Mar. 31, 2012 PUGET SOUND ENERGY, INC. [Member] SERP Pension Benefits [Member]	Mar. 31, 2013 PUGET SOUND ENERGY, INC. [Member] Other Benefit [Member]	Mar. 31, 2012 PUGET SOUND ENERGY, INC. [Member] Other Benefit [Member]
Components of net periodic benefit cost:
Service cost	$ (4,709)	$ (16,926)	$ (375)	$ (1,073)	$ (34)	$ (139)	$ 4,709	$ 4,235	$ 375	$ 268	$ 34	$ 38	$ 4,709	$ 4,235	$ 375	$ 268	$ 34	$ 38
Interest cost	(6,194)	(25,986)	(511)	(2,152)	(177)	(751)	6,194	6,442	511	538	176	187	6,194	6,442	511	538	176	187
Expected return on plan assets							(9,851)	(9,001)	0	0	(108)	(108)	(10,249)	(10,333)	0	0	(108)	(108)
Amortization of prior service cost							(495)	(495)	(4)	0	0	0	(393)	(393)	(4)	73	8	9
Amortization of net loss (gain)							650	149	365	176	17	9	5,085	3,717	548	358	(34)	(60)
Amortization of transition obligation													0	0	0	0	0	12
Defined Benefit Plan, Net Periodic Benefit Cost							$ 1,207	$ 1,330	$ 1,247	$ 982	$ 119	$ 126	$ 5,346	$ 3,668	$ 1,430	$ 1,237	$ 76	$ 78