Regulatory Matters	6 Months Ended
Regulatory Matters	Jun. 30, 2016
Schedule Of Regulatory Assets and Liabilities [Line Items]
Regulatory Matters	Regulatory Matters In November 2014, ALP filed a general tariff application ("GTA") asking the Alberta Utilities Commission ("AUC") to approve revenue requirements of C$811 million for 2015 and C$1.0 billion for 2016, primarily due to continued investment in capital projects as directed by the Alberta Electric System Operator. ALP amended the GTA in June 2015 to propose additional transmission tariff relief measures for customers and modifications to its capital structure. ALP also amended the GTA in October 2015 resulting in revenue requirements of C$672 million for 2015 and C$704 million for 2016. In May 2016, the AUC issued Decision 3524-D01-2016 pertaining to the 2015-2016 GTA. ALP filed its 2015-2016 GTA compliance filing in July 2016 in response to the AUC's decision pertaining to the 2015-2016 GTA. Following the AUC's assessment of whether the refiling complies with the decision, final transmission tariff rates for the 2015 and 2016 test years will be set, subject to further adjustment through the deferral account reconciliation process. The compliance filing asks the AUC to approve revenue requirements of C$599 million for 2015 and C$685 million for 2016. The decreased revenue requirements requested in the compliance filing, as compared to the original 2015-2016 GTA filing in November 2014, were based on changes to several key components considered in Decision 3524-D01-2016. Among other things, the AUC approved ALP's proposed immediate tariff relief of C$415 million for customers for 2015 and 2016, through (i) the discontinuance of construction work-in-progress ("CWIP") in rate base and the return to allowance for funds used during construction ("AFUDC") accounting effective January 1, 2015, resulting in a C$82 million reduction of revenue requirement and the refund of C$277 million previously collected as CWIP in rate base as part of ALP's transmission tariffs during 2011-2014 less related returns of C$12 million and (ii) the continued application of the future income tax method for calculating income taxes for 2015 and a change to the flow through method for calculating income taxes for 2016, resulting in further tariff relief of C$68 million. In July 2016, ALP also submitted a separate transmission tariff application requesting approval from the AUC to reduce the 2016 interim refundable tariff from C$61 million per month to C$12 million per month, for the period August 1, 2016 to December 31, 2016, in alignment with its compliance filing. The AUC previously approved in December 2015 ALP's request to continue its C$61 million monthly 2015 interim transmission tariff for the 2016 year. Operating revenue for the three- and six-month periods ended June 30, 2016, included one-time reductions totaling $225 million from the 2015-2016 GTA decision received in May 2016 at ALP. The decision requires ALP to refund $200 million to customers by the end of 2016 through reduced monthly billings for the change from receiving cash during construction for the return on CWIP in rate base to recording allowance for borrowed and equity funds used during construction related to construction expenditures during the 2011 to 2014 time period. This amount is offset in capitalized interest and allowance for equity funds in the Consolidated Statements of Operations. In addition, the decision requires ALP to change to the flow through method of recognizing income tax expense effective January 1, 2016. This change reduced operating revenue by $25 million for the three- and six-month periods ended June 30, 2016 with an offsetting impact to income tax expense in the Consolidated Statements of Operations.
Nevada Power Company [Member]
Schedule Of Regulatory Assets and Liabilities [Line Items]
Regulatory Matters	Regulatory Matters Deferred Energy Nevada statutes permit regulated utilities to adopt deferred energy accounting procedures. The intent of these procedures is to ease the effect on customers of fluctuations in the cost of purchased natural gas, fuel and electricity and are subject to annual prudency review by the Public Utilities Commission of Nevada ("PUCN"). Under deferred energy accounting, to the extent actual fuel and purchased power costs exceed fuel and purchased power costs recoverable through current rates that excess is not recorded as a current expense on the Consolidated Statements of Operations but rather is deferred and recorded as a regulatory asset on the Consolidated Balance Sheets. Conversely, a regulatory liability is recorded to the extent fuel and purchased power costs recoverable through current rates exceed actual fuel and purchased power costs. These excess amounts are reflected in quarterly adjustments to rates and recorded as cost of fuel, energy and capacity in future time periods.
Sierra Pacific Power Company [Member]
Schedule Of Regulatory Assets and Liabilities [Line Items]
Regulatory Matters	Regulatory Matters Deferred Energy Nevada statutes permit regulated utilities to adopt deferred energy accounting procedures. The intent of these procedures is to ease the effect on customers of fluctuations in the cost of purchased natural gas, fuel and electricity and are subject to annual prudency review by the Public Utilities Commission of Nevada ("PUCN"). Under deferred energy accounting, to the extent actual fuel and purchased power costs exceed fuel and purchased power costs recoverable through current rates that excess is not recorded as a current expense on the Consolidated Statements of Operations but rather is deferred and recorded as a regulatory asset on the Consolidated Balance Sheets. Conversely, a regulatory liability is recorded to the extent fuel and purchased power costs recoverable through current rates exceed actual fuel and purchased power costs. These excess amounts are reflected in quarterly adjustments to rates and recorded as cost of fuel, energy and capacity in future time periods.