New Accounting Pronouncements Revenue Recognition (Details)	Mar. 31, 2018
Revenue from Contract with Customer [Abstract]
Contracts with Customers from Rate-Regulated Sales of Electricity and Natural Gas	95.60%

Contracts with Customers from Rate-Regulated Sales of Electricity and Natural Gas

No definition available.

Name:	psd_ContractswithCustomersfromRateRegulatedSalesofElectricityandNaturalGas
Namespace Prefix:	psd_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant