Income taxes	3 Months Ended
Mar. 31, 2018
Income Tax Disclosure [Abstract]
Income taxes	Income taxes Staff Accounting Bulletin No. 118 (SAB No. 118). On December 22, 2017, the SEC staff issued SAB No. 118 to address the application of GAAP in situations when a registrant does not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the Tax Act. In 2017, the Company calculated its best estimate in accordance with its understanding of the law and available guidance. As of March 31, 2018, there were no adjustments made to provisional tax impacts previously recognized in the Company’s and Utilities financial statements. The provisional impacts will be updated when and if additional information is received as a result of changes in the Company and Utilities interpretations and assumptions, the issuance of Internal Revenue Service and Joint Committee on Taxation guidance, and actions the Company and Utilities may take as a result of the Tax Act. The provisional tax impacts will be finalized by the end of 2018.

Income taxes

3 Months Ended

Mar. 31, 2018

Staff Accounting Bulletin No. 118 (SAB No. 118). On December 22, 2017, the SEC staff issued SAB No. 118 to address the application of GAAP in situations when a registrant does not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the Tax Act. In 2017, the Company calculated its best estimate in accordance with its understanding of the law and available guidance. As of March 31, 2018, there were no adjustments made to provisional tax impacts previously recognized in the Company’s and Utilities financial statements. The provisional impacts will be updated when and if additional information is received as a result of changes in the Company and Utilities interpretations and assumptions, the issuance of Internal Revenue Service and Joint Committee on Taxation guidance, and actions the Company and Utilities may take as a result of the Tax Act. The provisional tax impacts will be finalized by the end of 2018.