Accounting for Derivative Instruments and Hedging Activities Contractual Contingent Liability (Details) - USD ($) $ in Thousands		Sep. 30, 2017	Dec. 31, 2016
External Credit Rating, Investment Grade [Member]
Derivative [Line Items]
Derivative, Credit Risk Exposure, Percentage		98.50%
External Credit Rating, Non Investment Grade [Member]
Derivative [Line Items]
Derivative, Credit Risk Exposure, Percentage		1.50%
Electric Portfolio [Member]
Derivative [Line Items]
Fair Value Liability	[1]	$ 34,066	$ 12,828
Posted Collateral		1,384	0
Additional Collateral, Aggregate Fair Value		6,113	4,894
Credit Rating [Member]
Derivative [Line Items]
Posted Collateral	[2]	1,400
Credit Rating [Member] | Electric Portfolio [Member]
Derivative [Line Items]
Fair Value Liability	[1],[2]	6,113	4,894
Posted Collateral	[2]	0	0
Additional Collateral, Aggregate Fair Value	[2]	6,113	4,894
Credit Rating [Member] | Natural Gas Portfolio [Member]
Derivative [Line Items]
Posted Collateral	[2]	1,000
Requested Credit for Adequate Assurance [Member] | Electric Portfolio [Member]
Derivative [Line Items]
Fair Value Liability	[1]	27,214	7,427
Posted Collateral		0	0
Additional Collateral, Aggregate Fair Value		0	0
Forward Value of Contract [Member] | Electric Portfolio [Member]
Derivative [Line Items]
Fair Value Liability	[1],[3]	739	507
Posted Collateral	[3]	1,384	0
Additional Collateral, Aggregate Fair Value	[3]	$ 0	$ 0

[1] 1 Represents the derivative fair value of contracts with contingent features for counterparties in net derivative liability positions. Excludes NPNS, accounts payable and accounts receivable.

[2] 2 Failure by PSE to maintain an investment grade credit rating from each of the major credit rating agencies provides counterparties a contractual right to demand collateral.

[3] 3 Collateral requirements may vary, based on changes in the forward value of underlying transactions relative to contractually defined collateral thresholds.