Retirement Benefits - Net Periodic Benefit Cost (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Qualified Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Noncurrent assets	$ 0	$ 42,404
Components of net periodic benefit cost:
Service cost	17,437	19,285	16,926
Interest cost	28,039	24,754	25,986
Expected return on plan assets	(42,464)	(39,095)	(36,203)
Amortization of prior service cost (credit)	(1,980)	(1,980)	(1,980)
Amortization of net loss	0	2,889	768
Net periodic benefit cost	1,032	5,853	5,497
Pension and Other Postretirement Defined Benefit Plans, Current Liabilities	0	0
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent	64,021	0
Defined Benefit Plan, Amounts Recognized in Balance Sheet	(64,021)	42,404
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Noncurrent assets	0	0
Components of net periodic benefit cost:
Service cost	1,042	1,498	1,073
Interest cost	2,310	2,045	2,152
Expected return on plan assets	0	0	0
Amortization of prior service cost (credit)	42	(17)	0
Amortization of net loss	913	1,461	702
Net periodic benefit cost	4,307	4,987	3,927
Pension and Other Postretirement Defined Benefit Plans, Current Liabilities	4,386	3,981
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent	51,469	43,298
Defined Benefit Plan, Amounts Recognized in Balance Sheet	(55,855)	(47,279)
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Noncurrent assets	0	0
Components of net periodic benefit cost:
Service cost	112	134	139
Interest cost	684	664	751
Expected return on plan assets	(535)	(436)	(435)
Amortization of prior service cost (credit)	0	0	0
Amortization of net loss	(393)	69	53
Net periodic benefit cost	(132)	431	508
Pension and Other Postretirement Defined Benefit Plans, Current Liabilities	355	421
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent	6,973	5,744
Defined Benefit Plan, Amounts Recognized in Balance Sheet	(7,328)	(6,165)
PUGET SOUND ENERGY, INC. \| Qualified Pension Benefits
Components of net periodic benefit cost:
Service cost	17,437	19,285	16,926
Interest cost	28,039	24,753	25,986
Expected return on plan assets	(43,252)	(40,685)	(41,533)
Amortization of prior service cost (credit)	(1,573)	(1,573)	(1,573)
Amortization of net loss	13,195	20,612	15,015
Amortization of transition obligation	0	0	0
Net periodic benefit cost	13,846	22,392	14,821
PUGET SOUND ENERGY, INC. \| Supplemental Employee Retirement Plan [Member]
Components of net periodic benefit cost:
Service cost	1,042	1,498	1,073
Interest cost	2,310	2,045	2,152
Expected return on plan assets	0	0	0
Amortization of prior service cost (credit)	44	(16)	293
Amortization of net loss	1,461	2,191	1,432
Amortization of transition obligation	0	0	0
Net periodic benefit cost	4,857	5,718	4,950
PUGET SOUND ENERGY, INC. \| Other Benefits
Components of net periodic benefit cost:
Service cost	112	134	139
Interest cost	684	664	751
Expected return on plan assets	(535)	(436)	(435)
Amortization of prior service cost (credit)	3	30	35
Amortization of net loss	(702)	(284)	(245)
Amortization of transition obligation	0	0	50
Net periodic benefit cost	$ (438)	$ 108	$ 295

The amount of gains or losses recognized in net periodic benefit cost.

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- Definition

The amount of the prior service cost or credit recognized in net periodic benefit cost relating to benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation.

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The amount of the transition obligation or asset recognized in net periodic benefit cost.

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The aggregate net amount recognized in the balance sheet associated with the defined benefit plan(s). Will normally be the same as the Defined Benefit Plan, Funded Status of Plan, Total.

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- Definition

The amount for overfunded plans recognized in the balance sheet as a noncurrent asset associated with a defined benefit pension plan or other postretirement defined benefit plan.

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- Definition

An amount calculated as a basis for determining the extent of delayed recognition of the effects of changes in the fair value of assets. The expected return on plan assets is determined based on the expected long-term rate of return on plan assets and the market-related value of plan assets.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 30

-Glossary Expected Return on Plan Assets

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- Definition

The increase in a defined benefit pension plan's projected benefit obligation or a defined benefit postretirement plan's accumulated postretirement benefit obligation due to the passage of time.

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- Definition

The total amount of net periodic benefit cost for defined benefit plans for the period. Periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments.

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- Definition

The actuarial present value of benefits attributed by the pension benefit formula to services rendered by employees during the period. The portion of the expected postretirement benefit obligation attributed to employee service during the period. The service cost component is a portion of the benefit obligation and is unaffected by the funded status of the plan.

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-Glossary Service Cost (Component of Net Periodic Pension Cost)

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- Definition

For a classified balance sheet, the amount recognized in balance sheet as a current liability associated with an underfunded defined benefit plan.

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-Glossary Current Liabilities

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- Definition

This represents the noncurrent liability for underfunded plans recognized in the balance sheet that is associated with the defined benefit pension plans and other postretirement defined benefit plans.

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