Commitments, Contingencies And Uncertainties	3 Months Ended
Mar. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments, Contingencies And Uncertainties	Commitments, Contingencies and Uncertainties For a full discussion of commitments and contingencies, see Note K of the Notes to Financial Statements in the 2017 Form 10-K. In addition, see Notes D and E above and Notes C and E of the Notes to Financial Statements in the 2017 Form 10-K regarding matters related to wholesale power sales contracts and transmission contracts subject to regulation and Palo Verde, including decommissioning, spent nuclear fuel and waste disposal, and liability and insurance matters. Power Purchase and Sale Contracts To supplement its own generation and operating reserve requirements and to meet required renewable portfolio standards, the Company engages in power purchase arrangements that may vary in duration and amount based on an evaluation of the Company's resource needs, the economics of the transactions and specific renewable portfolio requirements. For a discussion of power purchase and sale contracts that the Company has entered into with various counterparties, see Note K of the Notes to Financial Statements in the 2017 Form 10-K. Environmental Matters General. The Company is subject to extensive laws, regulations and permit requirements with respect to air and greenhouse gas emissions, water discharges, soil and water quality, waste management and disposal, natural resources and other environmental matters by federal, state, regional, tribal and local authorities. Failure to comply with such laws, regulations and requirements can result in actions by authorities or other third parties that might seek to impose on the Company administrative, civil and/or criminal penalties or other sanctions. In addition, releases of pollutants or contaminants into the environment can result in costly cleanup liabilities. These laws, regulations and requirements are subject to change through modification or reinterpretation, or the introduction of new laws and regulations, and as a result, the Company may face additional capital and operating costs to comply. Environmental Litigation and Investigations. Since July 2011, the U.S. Department of Justice, on behalf of the U.S. Environmental Protection Agency, and APS have been engaged in substantive settlement negotiations in an effort to resolve certain of the pending matters related to Four Corners. The allegations being addressed through settlement negotiations are that APS failed to obtain the necessary permits and install the controls necessary under the U.S. Clean Air Act ("CAA") to reduce sulfur dioxide, nitrogen oxides, and particulate matter, and that defendants failed to obtain an operating permit under Title V of the CAA that reflects applicable requirements imposed by law. On June 24, 2015, the parties filed with the U.S. District Court for New Mexico a settlement agreement resolving this matter. On August 17, 2015, the U.S. District Court for New Mexico entered the settlement agreement. The agreement imposes a total civil penalty payable by the co-owners of Four Corners collectively in the amount of $1.5 million, and it requires the co-owners to pay $6.7 million for environmental mitigation projects. At March 31, 2018, the Company has accrued its remaining unpaid share of approximately $0.2 million related to this matter.

Commitments, Contingencies and Uncertainties

For a full discussion of commitments and contingencies, see Note K of the Notes to Financial Statements in the 2017 Form 10-K. In addition, see Notes D and E above and Notes C and E of the Notes to Financial Statements in the 2017 Form 10-K regarding matters related to wholesale power sales contracts and transmission contracts subject to regulation and Palo Verde, including decommissioning, spent nuclear fuel and waste disposal, and liability and insurance matters.

Power Purchase and Sale Contracts

To supplement its own generation and operating reserve requirements and to meet required renewable portfolio standards, the Company engages in power purchase arrangements that may vary in duration and amount based on an evaluation of the Company's resource needs, the economics of the transactions and specific renewable portfolio requirements. For a discussion of power purchase and sale contracts that the Company has entered into with various counterparties, see Note K of the Notes to Financial Statements in the 2017 Form 10-K.

Environmental Matters

General. The Company is subject to extensive laws, regulations and permit requirements with respect to air and greenhouse gas emissions, water discharges, soil and water quality, waste management and disposal, natural resources and other environmental matters by federal, state, regional, tribal and local authorities. Failure to comply with such laws, regulations and requirements can result in actions by authorities or other third parties that might seek to impose on the Company administrative, civil and/or criminal penalties or other sanctions. In addition, releases of pollutants or contaminants into the environment can result in costly cleanup liabilities. These laws, regulations and requirements are subject to change through modification or reinterpretation, or the introduction of new laws and regulations, and as a result, the Company may face additional capital and operating costs to comply.

Environmental Litigation and Investigations. Since July 2011, the U.S. Department of Justice, on behalf of the U.S. Environmental Protection Agency, and APS have been engaged in substantive settlement negotiations in an effort to resolve certain of the pending matters related to Four Corners. The allegations being addressed through settlement negotiations are that APS failed to obtain the necessary permits and install the controls necessary under the U.S. Clean Air Act ("CAA") to reduce sulfur dioxide, nitrogen oxides, and particulate matter, and that defendants failed to obtain an operating permit under Title V of the CAA that reflects applicable requirements imposed by law. On June 24, 2015, the parties filed with the U.S. District Court for New Mexico a settlement agreement resolving this matter. On August 17, 2015, the U.S. District Court for New Mexico entered the settlement agreement. The agreement imposes a total civil penalty payable by the co-owners of Four Corners collectively in the amount of $1.5 million, and it requires the co-owners to pay $6.7 million for environmental mitigation projects. At March 31, 2018, the Company has accrued its remaining unpaid share of approximately $0.2 million related to this matter.