Entity tax identification number Entity Tax Identification Number Primary residence, borrowing term EBP, Note Receivable From Participant, Account, Primary Residence, Maximum Borrowing Term EBP, Note Receivable From Participant, Account, Primary Residence, Maximum Borrowing Term Employee Rollover EBP, Change in Net Asset Available for Benefit, Increase from Participant Contribution, Rollover Maximum Maximum [Member] Deemed Distributions EBP, Reconciliation to Form 5500, Change in Net Asset Available for Benefit, Increase (Decrease) from Deemed Distribution Legal Entity [Axis] Legal Entity [Axis] Statistical Measurement [Domain] Statistical Measurement [Domain] EBP, Description of Plan [Table] EBP, Description of Plan [Table] Mutual Funds Mutual Fund [Member] EBP, Related Party and Party-in-Interest Transactions [Table] EBP, Related Party and Party-in-Interest Transactions [Table] Pretax, maximum annual compensation to total compensation, percentage EBP, Participant Contribution, Pretax, Maximum Annual Compensation to Total Compensation, Percentage EBP, Fully Benefit-Responsive Investment Contract [Table] EBP, Fully Benefit-Responsive Investment Contract [Table] Total Deductions EBP, Change in Net Asset Available for Benefit, Decrease Self-Directed Brokerage Accounts EBP, Self-Directed Brokerage Account [Member] Maximum borrowing, amount EBP, Note Receivable from Participant, Account, Maximum Borrowing, Amount FAIR VALUE OF INVESTMENTS EBP, Investment, Fair Value and NAV [Text Block] Minimum borrowing, amount EBP, Note Receivable from Participant, Account, Minimum Borrowing, Amount Default period EBP, Note Receivable From Participant, Default Period EBP, Note Receivable From Participant, Default Period Total Investments at Fair Value EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value Repayment period EBP, Note Receivable From Participant, Repayment Period EBP, Note Receivable From Participant, Repayment Period Level 1 Fair Value, Inputs, Level 1 [Member] EBP, Reconciliation of Financial Statement to Form 5500 EBP, Reconciliation of Financial Statement to Form 5500 [Table Text Block] Catch-up contribution age EBP, Employer Contribution, Minimum Catch-Up Contributions Age EBP, Employer Contribution, Minimum Catch-Up Contributions Age EBP, Investment, Fair Value and NAV [Abstract] ASSETS EBP, Asset [Abstract] Statistical Measurement [Axis] Statistical Measurement [Axis] ADDITIONS: EBP, Change in Net Asset Available for Benefit, Increase [Abstract] EBP, Statement of Change in Net Asset Available for Benefit [Table] EBP, Statement of Change in Net Asset Available for Benefit [Table] Payment of Benefits EBP, Payment to Participant [Policy Text Block] Amendment Flag Amendment Flag Deemed Distributions EBP, Reconciliation to Form 5500, Net Asset Available for Benefit, Deemed Distribution Basis of Accounting EBP, Basis of Accounting [Policy Text Block] EBP, Schedule of Asset Held for Investment [Table] EBP, Schedule of Asset Held for Investment [Table] Investment, number of shares (in shares) EBP, Investment, Number of Shares Maximum contribution to investment, percentage EBP, Participant Contribution, Maximum Contribution To Investment, Percentage EBP, Participant Contribution, Maximum Contribution To Investment, Percentage EBP, Description of Plan and Accounting Change [Abstract] Receivables EBP, Receivable [Abstract] EBP, Investment, Fair Value and NAV EBP, Investment, Fair Value and NAV [Table Text Block] EBP, Contribution, Participating Employer [Domain] EBP, Contribution, Participating Employer [Domain] Investments [Domain] Investments [Domain] In-service distribution age EBP, In-Service Distribution Age EBP, In-Service Distribution Age Use of Estimate EBP, Use of Estimate [Policy Text Block] SCHEDULE H, LINE 4i - SCHEDULE OF ASSETS (HELD AT END OF YEAR) EBP, Schedule of Asset Held for Investment [Text Block] Cover [Abstract] EBP, Contribution, Participating Employer [Axis] EBP, Contribution, Participating Employer [Axis] Common/Collective Trust Fair Value Adjustment EBP, Reconciliation to Form 5500, Change in Net Asset Available for Benefit, Increase (Decrease) from Contract Value to Current Value RISKS AND UNCERTAINTIES EBP, Risk and Uncertainty [Text Block] Employer EBP, Change in Net Asset Available for Benefit, Increase from Employer Contribution, Cash Minimum Minimum [Member] Interest Income on Notes Receivable from Participants EBP, Change in Net Asset Available for Benefit, Increase from Interest Income on Note Receivable from Participant Investment Type [Axis] Investment Type [Axis] Total Contributions EBP, Change in Net Asset Available for Benefit, Increase from Contribution Employee 401(k) Deferral EBP, Change in Net Asset Available for Benefit, Increase from Participant Contribution, Excluding Rollover Net Appreciation in Fair Value of Investments EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Gain (Loss) on Investment Interest and Dividends EBP, Change in Net Asset Available for Benefit, Increase from Interest and Dividend Income on Investment EBP, Description of Plan [Line Items] EBP, Description of Plan [Line Items] Plan number EBP, Plan Number EBP, Investment, Fair Value and NAV [Line Items] EBP, Investment, Fair Value and NAV [Line Items] DESCRIPTION OF PLAN EBP, Description of Plan [Text Block] EBP, Statement of Change in Net Asset Available for Benefit [Line Items] EBP, Statement of Change in Net Asset Available for Benefit [Line Items] EBP, Statement of Net Asset Available for Benefit [Table] EBP, Statement of Net Asset Available for Benefit [Table] Basis spread on variable rate EBP, Participant Loan, Basis Spread On Variable Rate EBP, Participant Loan, Basis Spread On Variable Rate Common/Collective Trust Fair Value Adjustment EBP, Reconciliation to Form 5500, Net Asset Available for Benefit, Contract Value to Current Value Adjustment EBP, Schedule of Asset Held for Investment [Line Items] EBP, Schedule of Asset Held for Investment [Line Items] Contributions EBP, Contribution [Policy Text Block] Fortis Inc. Common Stock EBP, Employer, Common Stock [Member] EBP, Schedule of Asset Held for Investment [Abstract] EBP, Accounting Policy [Table] EBP, Accounting Policy [Table] Total Additions EBP, Change in Net Asset Available for Benefit, Increase Allowance for credit loss EBP, Note Receivable from Participant, Allowance for Credit Loss Investment Income EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Income (Loss) on Investment [Abstract] Investment, Identifier [Axis] Investment, Identifier [Axis] EBP 007 EBP 007 [Member] EBP 007 Involuntary cash-out limit EBP, Involuntary Cash-out Limit EBP, Involuntary Cash-out Limit Employer contribution vesting percentage EBP, Employer Contribution Vesting Percentage Company contribution and/ or investment earning percentage vesting to the participant in Company Matching Contributions, Fixed Rate Contributions, Discretionary Profit-Sharing Contributions, Qualified Non-Elective Contributions, and Disability Contributions, upon completion of minimum service period or attainment of maximum vesting age Administrative Expenses EBP, Change in Net Asset Available for Benefit, Decrease from Administrative Expense EBP, Asset Held for Investment EBP, Asset Held for Investment Document Information [Line Items] Document Information [Line Items] EBP, Risk and Uncertainty [Line Items] EBP, Risk and Uncertainty [Line Items] EBP, Risk and Uncertainty [Table] EBP, Risk and Uncertainty [Table] Participant compensation matched, percentage EBP, Employer Contribution, Participant Compensation Matched, Percentage EBP, Statement of Change in Net Asset Available for Benefit [Abstract] Level 2 Fair Value, Inputs, Level 2 [Member] Participant loan, cost EBP, Asset Held for Investment, Participant Loan, Cost EBP, Asset Held for Investment, Participant Loan, Cost Net Increase (Decrease) in Net Assets Available for Benefits per Form 5500 EBP, Form 5500 Caption, Net Income (Loss) EBP, Fully Benefit-Responsive Investment Contract [Line Items] EBP, Fully Benefit-Responsive Investment Contract [Line Items] EBP, Tax Status [Table] EBP, Tax Status [Table] Net Increase (Decrease) in Net Assets Available for Benefits Net Increase (Decrease) in Net Assets Available for Benefits EBP, Change in Net Asset Available for Benefit, Increase (Decrease) PARTY-IN-INTEREST AND RELATED PARTY TRANSACTIONS EBP, Related Party and Party-in-Interest Transactions [Text Block] EBP, Related Party and Party-in-Interest Transactions [Abstract] EBP, Accounting Policy, Accounting Standard Update, and Change in Accounting Principle [Abstract] Total Receivables EBP, Receivable Automatic deferral rate EBP, Participant Contribution, Automatic, Deferral Rate Investments EBP, Investment, Fair Value [Abstract] Increase from dividend income on investment EBP, Change in Net Asset Available for Benefit, Increase from Dividend Income on Investment Benefits Paid to Participants EBP, Change in Net Asset Available for Benefit, Decrease from Payment to Participant Total Assets EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Current Value Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Maximum percent of contribution of account balance EBP, Participate Contribution, Maximum Balance Of Investment, Percent EBP, Participate Contribution, Maximum Balance Of Investment, Percent EBP, Statement of Net Asset Available for Benefit [Abstract] EBP, Accounting Policy [Line Items] EBP, Accounting Policy [Line Items] EBP, Tax Status [Abstract] EBP, Reconciliation of Financial Statement to Form 5500 [Table] EBP, Reconciliation of Financial Statement to Form 5500 [Table] EBP, Reconciliation of Financial Statement to Form 5500 [Line Items] EBP, Reconciliation of Financial Statement to Form 5500 [Line Items] Administrative Expenses EBP, Expense [Policy Text Block] RECONCILIATION OF FINANCIAL STATEMENTS TO FORM 5500 EBP, Reconciliation of Financial Statement to Form 5500 [Text Block] Notes Receivable from Participants: EBP, Asset Held for Investment, Participant Loan, after Deemed Distribution Investment Valuation and Income Recognition EBP, Investment [Policy Text Block] Total Fair Value, Inputs, Level 1, Level 2, and Level 3 [Member] Document Type Document Type PLAN TERMINATION EBP, Plan Termination [Text Block] EBP, Tucson Electric Power Company EBP, Tucson Electric Power Company [Member] EBP, Tucson Electric Power Company Entity Central Index Key Entity Central Index Key Participant loan, interest rate EBP, Asset Held for Investment, Participant Loan, Interest Rate EBP, Reconciliation of Financial Statement to Form 5500 [Abstract] Common/Collective Trusts Common Collective Trust [Member] EBP, Risk and Uncertainty [Abstract] EBP, Tax Status [Line Items] EBP, Tax Status [Line Items] EBP, Subsequent Event [Table] EBP, Subsequent Event [Table] General loan, borrowing term EBP, Note Receivable From Participant, General Loan, Maximum Borrowing Term EBP, Note Receivable From Participant, General Loan, Maximum Borrowing Term DEDUCTIONS: EBP, Change in Net Asset Available for Benefit, Decrease [Abstract] Notes Receivable from Participants EBP, Note Receivable from Participant Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES EBP, Summary of Accounting Policy [Text Block] Entity Registrant Name Entity Registrant Name Cost basis EBP, Investment, Excluding Plan Interest in Master Trust, Cost Subsequent Events EBP, Subsequent Event [Policy Text Block] Plan Tax Status EBP, Tax Status [Text Block] Maximum borrowing, to total account, percentage EBP, Note Receivable from Participant, Account, Maximum Borrowing, to Total Account, Percentage EBP, Subsequent Event [Line Items] EBP, Subsequent Event [Line Items] Document Information [Table] Document Information [Table] EBP, UNS Gas, Inc. and UNS Electric, Inc. EBP, UNS Gas, Inc. and UNS Electric, Inc. [Member] EBP, UNS Gas, Inc. and UNS Electric, Inc. Severance of employment age EBP, Severance Of Employment Age EBP, Severance Of Employment Age Note Receivable from Participants EBP, Note Receivable from Participant [Policy Text Block] Total Investment Income EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Income (Loss) on Investment EBP, Related Party and Party-in-Interest Transactions [Line Items] EBP, Related Party and Party-in-Interest Transactions [Line Items] Level 3 Fair Value, Inputs, Level 3 [Member] Non-elective employer contribution, percentage EBP, Non-Elective Employer Contribution, Percentage EBP, Non-Elective Employer Contribution, Percentage Net assets available for benefits Net Assets Available for Benefits, Beginning of Year Net Assets Available for Benefits, End of Year Net Assets Available for Benefits EBP, Net Asset Available for Benefit Entity [Domain] Entity [Domain] Contributions EBP, Change in Net Asset Available for Benefit, Increase from Contribution [Abstract] Matching percentage EBP, Employer Contribution, Matching Percentage Net Assets Available for Benefits per Form 5500 EBP, Form 5500 Caption, Net Assets NAV Fair Value Measured at Net Asset Value Per Share [Member] EBP, Investment, Fair Value and NAV [Table] EBP, Investment, Fair Value and NAV [Table] EBP, Statement of Net Asset Available for Benefit [Line Items] EBP, Statement of Net Asset Available for Benefit [Line Items]