Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Mar. 31, 2018
Income Taxes
Reduction in net deferredincome tax liabilities	$ 1,140,000
Regulatory liabilities, non-current	2,452,536	$ 2,415,417
Arizona Public Service Company
Income Taxes
Reduction in net deferredincome tax liabilities	1,140,000
Regulatory liabilities, non-current	2,452,536	2,415,417
Gross-up for revenue requirement of rate regulation	377,000
Excess deferred income taxes - Tax Cuts and Jobs Act
Income Taxes
Regulatory liabilities, non-current	1,520,274	$ 1,519,224
Excess deferred income taxes - Tax Cuts and Jobs Act | Arizona Public Service Company
Income Taxes
Regulatory liabilities, non-current	$ 1,520,000