Regulation and Rates Public Utilities, Regulatory Proceeding (Tables)

3 Months Ended

12 Months Ended

Mar. 31, 2017

Dec. 31, 2016

Decoupling Mechanism [Member]

Regulation and Rates [Line Items]

Schedule of Deferrals Not Included in Rate Increases [Table Text Block]

As noted earlier, the Company is also limited to a 3.0% annual decoupling related cap on increases in total revenue. This limitation has been triggered as follows for natural gas with no impacts to electric:

Effective Date Accrued Through	Deferrals not Included in Annual Rate Increases (Dollars in Millions)
Natural Gas:
2016	$47.4
2015	28.7

Schedule of Graduated Scale of Rate Adjustment Mechanisms [Table Text Block]

The Washington Commission approved the following PSE requests to change rates under its electric and natural gas decoupling mechanisms:

Effective Date	Average Percentage Increase (Decrease) in Rates	Increase (Decrease) in Revenue (Dollars in Millions)
Electric:
May 1, 2017	2.0%	$41.9
May 1, 2016	1.0	20.8
Natural Gas:
May 1, 2017	2.4%	$22.4
May 1, 2016	2.8	25.4

Schedule of Reduction in Rate Increases due to Excess Earnings [Table Text Block]

In addition, PSE filed with the Washington Commission the following reductions in decoupling deferrals due to the earnings sharing threshold for the electric and natural gas rate increases above:

Effective Date	Included in Rates Effective in	Reduction in Rate Increases due to Excess Earnings (Dollars in Millions)
Electric:
2016	May 2017	$11.9
2015	May 2016	11.9
Natural Gas:
2016	May 2017	$2.2
2015	May 2016	5.5

PCA Mechanism [Member] | Electric [Member]

Regulation and Rates [Line Items]

Schedule of Effects on Annual Revenue Due to Approved Rate Adjustments [Table Text Block]

On August 7, 2015, the Washington Commission issued an order approving the settlement proposing changes to the PCA mechanism. The settlement agreement took effect January 1, 2017 and applies the following graduated scale:

Annual Power Cost Variability	Company's Share		Customers' Share
Over or Under Collection	Over	Under	Over	Under
Over or Under Collected by up to $17 million	100%	100%	—%	—%
Over or Under Collected by between $17 million - $40 million	35	50	65	50
Over or Under Collected beyond $40 + million	10	10	90	90

The graduated scale that was applicable through December 31, 2016 was as follows:

Annual Power Cost Variability	Company’s Share	Customers' Share
+/- $20 million	100%	—%
+/- $20 million - $40 million	50	50
+/- $40 million - $120 million	10	90
+/- $120 + million	5	95

Property tax tracker [Member] [Domain] | Natural Gas [Member]

Regulation and Rates [Line Items]

Schedule of Effects on Annual Revenue Due to Approved Rate Adjustments [Table Text Block]

The following table sets forth property tax tracker mechanism rate adjustments approved by the Washington Commission and the corresponding annual impact on PSE’s revenue based on the effective dates:

Effective Date	Average Percentage Increase (Decrease) in Rates	Increase (Decrease) in Revenue (Dollars in Millions)
May 1, 2017	(0.1)%	$(1.1)
May 1, 2016	0.4	3.5

Property tax tracker [Member] [Domain] | Electric [Member]

Regulation and Rates [Line Items]

Schedule of Effects on Annual Revenue Due to Approved Rate Adjustments [Table Text Block]

The following table sets forth property tax tracker mechanism rate adjustments approved by the Washington Commission and the corresponding annual impact on PSE’s revenue based on the effective dates:

Effective Date	Average Percentage Increase (Decrease) in Rates	Increase (Decrease) in Revenue (Dollars in Millions)
May 1, 2017	(0.04)%	$(0.9)
May 1, 2016	0.3	5.7

Conservation Rider [Member] | Natural Gas [Member]

Regulation and Rates [Line Items]

Schedule of Effects on Annual Revenue Due to Approved Rate Adjustments [Table Text Block]

The following table sets forth conservation rider rate adjustments approved by the Washington Commission and the corresponding annual impact on PSE’s revenue based on the effective dates:

Effective Date	Average Percentage Increase (Decrease) in Rates	Increase (Decrease) in Revenue (Dollars in Millions)
May 1, 2017	(0.1)%	$(1.0)
May 1, 2016	0.3	2.9

Conservation Rider [Member] | Electric [Member]

Regulation and Rates [Line Items]

Schedule of Effects on Annual Revenue Due to Approved Rate Adjustments [Table Text Block]

The following table sets forth conservation rider rate adjustments approved by the Washington Commission and the corresponding annual impact on PSE’s revenue based on the effective dates:

Effective Date	Average Percentage Increase (Decrease) in Rates	Increase (Decrease) in Revenue (Dollars in Millions)
May 1, 2017	0.7%	$16.5
May 1, 2016	(0.5)	(11.7)

PCORC [Domain] | Electric [Member]

Regulation and Rates [Line Items]

Schedule of Effects on Annual Revenue Due to Approved Rate Adjustments [Table Text Block]

The following table sets forth the updated compliance filing rate adjustment that became effective on December 1, 2016 by operation of law and the corresponding annual impact on PSE's revenue based on the effective dates:

Effective Date	Average Percentage Increase (Decrease) in Rates	Increase (Decrease) in Revenue (Dollars in Millions)
December 1, 2016	(1.7)%	$(37.3)

Treasury Grants [Member] | Electric [Member]

Regulation and Rates [Line Items]

Schedule of Effects on Annual Revenue Due to Approved Rate Adjustments [Table Text Block]

The following table sets forth the Federal Incentive Tracker Tariff revenue requirement approved by the Washington Commission and the corresponding annual impact on PSE’s revenue based on the effective dates:

Effective Date	Average Percentage Increase (Decrease) in Rates from prior year	Total credit to be passed back to eligible customers (Dollars in Millions)
January 1, 2017	0.3%	$(51.7)
January 1, 2016	(0.2)	(57.3)

Cost recovery mechanism [Member] | Natural Gas [Member]

Regulation and Rates [Line Items]

Schedule of Effects on Annual Revenue Due to Approved Rate Adjustments [Table Text Block]

The following table sets forth CRM rate adjustment approved by the Washington Commission and the corresponding annual impact on PSE’s revenue based on the effective dates:

Effective Date	Average Percentage Increase (Decrease) in Rates	Increase (Decrease) in Revenue (Dollars in Millions)
November 1, 2016	0.6%	$5.6

Purchased Gas Adjustment (PGA) [Member] | Natural Gas [Member]

Regulation and Rates [Line Items]

Schedule of Effects on Annual Revenue Due to Approved Rate Adjustments [Table Text Block]

The following table sets forth the PGA rate adjustment approved by the Washington Commission and the corresponding annual impact on PSE’s revenue based on the effective dates:

Effective Date	Average Percentage Increase (Decrease) in Rates	Increase (Decrease) in Revenue (Dollars in Millions)
November 1, 2016	(0.4)%	$(4.1)