Summary of Significant Accounting Policies - Narrative (Details) $ / shares in Units, $ in Millions	1 Months Ended	12 Months Ended			36 Months Ended
	May 31, 2014 $ / kWh	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2017 USD ($) $ / shares shares	Jul. 06, 2016
Approximate remaining average useful lives of utility property
Cost of services, depreciation		$ 453	$ 422	$ 430
Depreciation rates (as a percent)		2.80%	2.66%	2.74%
Allowance for Funds Used During Construction
Composite rate used to calculate AFUDC (as a percent)		6.68%	7.17%	8.02%
Income Taxes
Percent likelihood largest tax benefit amount is realized (greater than)		50.00%
Intangible Assets
Amortization expense		$ 72	$ 58	$ 58
Estimated amortization expense on existing intangible assets over the next five years
2018		53			$ 53
2019		38			38
2020		28			28
2021		22			22
2022		$ 17			$ 17
Remaining amortization period for intangible assets		6 years
Pinnacle West
Preferred Stock
Preferred stock, shares authorized (in shares) | shares		10,000,000			10,000,000
ARIZONA PUBLIC SERVICE COMPANY
Nuclear Fuel
Charges for the permanent disposal of spent nuclear fuel (in dollars per kWh) | $ / kWh	0.001
Preferred Stock
Preferred stock, shares authorized (in shares) | shares		15,535,000			15,535,000
Preferred stock par or stated value per share 1 (in dollars per share) | $ / shares		$ 25			$ 25
Preferred stock par or stated value per share 2 (in dollars per share) | $ / shares		50			50
Preferred stock par or stated value per share 3 (in dollars per share) | $ / shares		$ 100			$ 100
Minimum
Approximate remaining average useful lives of utility property
Depreciation rates (as a percent)					0.18%
Maximum
Approximate remaining average useful lives of utility property
Depreciation rates (as a percent)					16.44%
Investments
Ownership percentage for classification as cost method investments by El Dorado		20.00%
Fossil plant
Approximate remaining average useful lives of utility property
Average useful life		21 years
Nuclear plant
Approximate remaining average useful lives of utility property
Average useful life		26 years
Other generation
Approximate remaining average useful lives of utility property
Average useful life		25 years
Transmission
Approximate remaining average useful lives of utility property
Average useful life		38 years
Distribution
Approximate remaining average useful lives of utility property
Average useful life		33 years
General plant
Approximate remaining average useful lives of utility property
Average useful life		6 years
El Paso's Interest in Four Corners | 4CA
Utility Plant and Depreciation [Line Items]
Ownership interest acquired (as a percent)		7.00%			7.00%	7.00%