Debt Disclosure [Abstract]
Schedule of Long-term Debt Instruments [Table]
Schedule of Long-term Debt Instruments [Table]
Debt Instrument [Axis]
Debt Instrument [Axis]
Debt Instrument, Name [Domain]
Debt Instrument, Name [Domain]
Unsecured 8.50% Senior Notes, due March 2019
Unsecured Senior Notes Due 2019 [Member]
Unsecured 8.50% Senior Notes, due 2019
Unsecured 3.00% Senior Notes, due 2027
Unsecured Senior Notes Due 2027 [Member]
Unsecured Senior Notes Due 2027 [Member]
Unsecured 5.95% Senior Notes, due 2034
Unsecured Senior Notes Due 2034 [Member]
Unsecured 5.95% Senior Notes, due 2034
Unsecured 5.50% Senior Notes, due 2041
Unsecured Senior Notes Due 2041 [Member]
Unsecured 5.50% Senior Notes, due 2041
Unsecured 4.15% Senior Notes, due 2043
Unsecured Senior Notes Due 2043 [Member]
Unsecured 4.15% Senior Notes, due 2043
Unsecured 4.125% Senior Notes, due 2044
Unsecured Senior Notes Due 2044 [Member]
Unsecured 4.125% Senior Notes, Due 2044 [Member]
Medium-term note Series A, 1995-1, 6.67%, due 2025
Medium Term Notes Due 2025 [Member]
Series A, 1995-1, 6.67%, due 2025
Unsecured 6.75% Debentures, due 2028
Unsecured Debentures Due 2028 [Member]
Unsecured 6.75% Debentures, due 2028
Floating-rate term loan, due September 2019
Multi-Draw Term Loan [Member]
The three year, $200 million multi-draw term loan agreement with three lenders.
Unsecured 4.30% Senior Notes, due 2048
Unsecured 4.30% Senior Notes, due 2048 [Member]
Unsecured 4.30% Senior Notes, due 2048 [Member]
Unsecured 4.125% Senior Notes, due 2049
Unsecured 4.125% Senior Notes, due 2049 [Member]
Unsecured 4.125% Senior Notes, due 2049 [Member]
Debt Instrument [Line Items]
Debt Instrument [Line Items]
Total long-term debt
Long-term Debt, Gross
Interest rate
Debt Instrument, Interest Rate, Stated Percentage
Original issue (premium) / discount on unsecured senior notes and debentures
Debt Instrument, Unamortized Discount (Premium), Net
Debt issuance cost
Debt Issuance Costs, Net
Current maturities
Long-term Debt, Current Maturities
Long-term debt
Long-term Debt, Excluding Current Maturities
Maximum borrowing capacity
Debt Instrument, Face Amount
Accounting Policies [Abstract]
Schedule of Regulatory Assets
Schedule of Regulatory Assets [Table Text Block]
Schedule of Regulatory Liabilities
Schedule of Regulatory Liabilities [Table Text Block]
Statement of Cash Flows [Abstract]
Cash Flows From Operating Activities
Net Cash Provided by (Used in) Operating Activities, Continuing Operations [Abstract]
Net income
Net Income (Loss) Attributable to Parent
Adjustments to reconcile net income to net cash provided by operating activities:
Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]
Depreciation and amortization expense
Depreciation, Depletion and Amortization
Deferred income taxes
Deferred Income Tax Expense (Benefit)
One-time income tax benefit
One Time Income Tax Benefit TCJA
Amount of the one-time income tax benefit as a result of the revaluation of the net deferred tax liability not associated with the Company’s regulated operations using the reduced federal statutory tax rate due to the Tax Cuts and Jobs Act of 2017 (the TCJA).
Other
Other Noncash Income (Expense)
Net assets / liabilities from risk management activities
Increase (Decrease) in Commodity Contract Assets and Liabilities
Net change in operating assets and liabilities
Increase (Decrease) in Operating Assets
Net cash provided by operating activities
Net Cash Provided by (Used in) Operating Activities
Cash Flows From Investing Activities
Net Cash Provided by (Used in) Investing Activities [Abstract]
Capital expenditures
Payments to Acquire Productive Assets
Proceeds from the sale of discontinued operations
Cash Provided by (Used in) Investing Activities, Discontinued Operations
Debt and equity securities activities, net
Payments for (Proceeds from) Investments
Other, net
Payments for (Proceeds from) Other Investing Activities
Net cash used in investing activities
Net Cash Provided by (Used in) Investing Activities
Cash Flows From Financing Activities
Net Cash Provided by (Used in) Financing Activities [Abstract]
Net decrease in short-term debt
Proceeds from (Repayments of) Short-term Debt
Net proceeds from equity offering
Proceeds from Issuance of Common Stock
Issuance of common stock through stock purchase and employee retirement plans
Proceeds from Issuance or Sale of Equity
Proceeds from issuance of long-term debt
Proceeds from Issuance of Long-term Debt
Settlements of interest rate swap
Payments for (Proceeds from) Hedge, Financing Activities
Repayments of Long-term Debt
Repayments of Long-term Debt
Cash dividends paid
Payments of Ordinary Dividends, Common Stock
Debt issuance costs
Payments of Debt Issuance Costs
Other
Proceeds from (Payments for) Other Financing Activities
Net cash provided by (used in) financing activities
Net Cash Provided by (Used in) Financing Activities
Net increase in cash and cash equivalents
Cash and Cash Equivalents, Period Increase (Decrease)
Cash and cash equivalents at beginning of period
Cash and Cash Equivalents, at Carrying Value
Cash and cash equivalents at end of period
Equity [Abstract]
Schedule of Stockholders Equity
Schedule of Stockholders Equity [Table Text Block]
Schedule of Accumulated Other Comprehensive Income (Loss)
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative [Table]
Derivative [Table]
Expected Recognition in Earnings of Deferred Gain Losses Financial Instruments [Axis]
Expected Recognition in Earnings of Deferred Gain Losses Financial Instruments [Axis]
-- None. No documentation exists for this element. --
Expected Recognition in Earnings of Deferred Gain Losses Financial Instruments [Domain]
Expected Recognition in Earnings of Deferred Gain Losses Financial Instruments [Domain]
-- None. No documentation exists for this element. --
Next twelve months
Next Twelve Months [Member]
-- None. No documentation exists for this element. --
Thereafter
Thereafter [Member]
-- None. No documentation exists for this element. --
Derivative [Line Items]
Derivative [Line Items]
Interest Rate Agreements
Expected Recognition in Earnings of Deferred Gain (Losses), Interest Rate Agreements
The expected recognition in earnings of deferred gains (losses) recorded in AOCI associated with our interest rate agreements.
Statement of Financial Position [Abstract]
Common stock stated value (USD per share)
Common Stock, Par or Stated Value Per Share
Common stock authorized (in shares)
Common Stock, Shares Authorized
Common stock issued (in shares)
Common Stock, Shares, Issued
Common stock outstanding (in shares)
Common Stock, Shares, Outstanding
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Business
Nature of Operations [Text Block]
Revenue from Contract with Customer [Abstract]
Revenue from Contract with Customer
Revenue from Contract with Customer [Text Block]
Number of customers serviced
Number Of Customers, Regulated Distribution
Number Of Customers, Regulated Distribution
Number of regulated distribution divisions
Number Of Divisions, Regulated Distribution
Represents the number of regulated distribution divisions.
Number of states with service areas
Number of States in which Entity Operates
Financial Instruments
Derivative Instruments and Hedging Activities Disclosure [Text Block]
Fair Value Disclosures [Abstract]
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]
Schedule of Carrying Values and Estimated Fair Values of Debt Instruments
Schedule of Carrying Values and Estimated Fair Values of Debt Instruments [Table Text Block]
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block]
Schedule of Cash Flow Hedges Included in Accumulated Other Comprehensive Income (Loss)
Schedule of Cash Flow Hedges Included in Accumulated Other Comprehensive Income (Loss) [Table Text Block]
Schedule Of Expected Deferred Gains (Losses) Recognition
Schedule Of Expected Deferred Gains (Losses) Recognition Table [Text Block]
Tabular disclosure of the expected recognition in earnings of the deferred losses recorded in accumulated other comprehensive gains/(losses) associated with cash flow hedges.
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies
Commitments and Contingencies Disclosure [Text Block]
Retirement Benefits, Description [Abstract]
Schedule of Net Benefit Costs
Schedule of Net Benefit Costs [Table Text Block]
Risks and Uncertainties [Abstract]
Concentration of Credit Risk
Concentration Risk Disclosure [Text Block]
Fair Value Measurements
Fair Value Disclosures [Text Block]
Disaggregation of Revenue
Disaggregation of Revenue [Table Text Block]
Fair Values Derivatives Balance Sheet Location By Derivative Contract Type By Hedging Designation [Table]
Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table]
Hedging Designation [Axis]
Hedging Designation [Axis]
Hedging Designation [Domain]
Hedging Designation [Domain]
Designated as Hedging Instrument
Designated as Hedging Instrument [Member]
Not Designated as Hedging Instrument
Not Designated as Hedging Instrument [Member]
Balance Sheet Location [Axis]
Balance Sheet Location [Axis]
Balance Sheet Location [Domain]
Balance Sheet Location [Domain]
Other Current Assets
Other Current Assets [Member]
Other Current Liabilities
Other Current Liabilities [Member]
Deferred Charges and Other Assets
Other Noncurrent Assets [Member]
Deferred Credits and Other Liabilities
Other Noncurrent Liabilities [Member]
Derivative Instrument [Axis]
Derivative Instrument [Axis]
Derivative Contract [Domain]
Derivative Contract [Domain]
Interest rate agreements
Interest Rate Contract [Member]
Commodity contracts
Commodity Contract [Member]
Derivatives Fair Value [Line Items]
Derivatives, Fair Value [Line Items]
Gross Financial Instruments, Assets
Derivative Asset, Fair Value, Gross Asset
Contract Netting
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset
Net Financial Instruments, Assets
Derivative Asset, Net of Contract Netting
Fair value, after the effects of contract netting under the master netting arrangements and prior to the offset of cash collateral, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.
Gross Financial Instruments, Liabilities
Derivative Liability, Fair Value, Gross Liability
Cash collateral
Derivative, Collateral, Right to Reclaim Cash
Net Financial Instruments, Liabilities
Derivative Liability, Net of Contract Netting
Fair value, after the effects of contract netting under the master netting arrangements and prior to the offset of cash collateral, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Table]
Fair Value Measurements, Recurring and Nonrecurring [Table]
Fair Value By Fair Value Hierarchy Level [Axis]
Fair Value Hierarchy and NAV [Axis]
Fair Value Measurements Fair Value Hierarchy [Domain]
Fair Value Hierarchy and NAV [Domain]
Fair Value Inputs Level 1
Fair Value, Inputs, Level 1 [Member]
Fair Value Inputs Level 2
Fair Value, Inputs, Level 2 [Member]
Fair Value Inputs Level 3
Fair Value, Inputs, Level 3 [Member]
Financial Instrument [Axis]
Financial Instrument [Axis]
Financial Instruments [Domain]
Financial Instruments [Domain]
Registered investment companies
Equity Securities [Member]
Bond mutual funds
Fixed Income Funds [Member]
Bonds
Debt Securities [Member]
Money market funds
Money Market Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments gross assets
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement
Netting and Cash Collateral
Financial instruments net assets
Derivative Asset
Debt Securities, Available-for-sale
Debt Securities, Available-for-sale
Equity Securities
Equity Securities, FV-NI
Debt and equity securities
Debt and equity securities
Total Debt and equity securities
Total assets
Assets, Fair Value Disclosure
Financial instruments gross liability
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement
Netting and Cash Collateral
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset
Financial instruments net liability
Derivative Liability
Income Tax Disclosure [Abstract]
Income Tax Examination [Table]
Income Tax Examination [Table]
Regulatory Liability [Axis]
Regulatory Liability [Axis]
Regulatory Liability [Domain]
Regulatory Liability [Domain]
Regulatory cost of service reserve
Regulatory Cost of Service Reserve [Member]
Regulatory Cost of Service Reserve [Member]
Range [Axis]
Range [Axis]
Range [Domain]
Range [Domain]
Minimum
Minimum [Member]
Maximum
Maximum [Member]
Income Tax Examination [Line Items]
Income Tax Examination [Line Items]
TCJA Income Tax Benefit
Tax Cuts and Jobs Act of 2017 Change in Tax Rate Income Tax Benefit
Tax Cuts and Jobs Act of 2017 Change in Tax Rate Income Tax Benefit
Regulated operations recorded as a regulatory liability
Tax Cuts and Jobs Act of 2017, Change in Tax Rate, Regulatory Liability
Tax Cuts and Jobs Act of 2017, Change in Tax Rate, Regulatory Liability
TCJA additional liability due to tax rates used in rates
Tax Cuts and Jobs Act of 2017 additional liability due tax rates used in rates
Tax Cuts and Jobs Act of 2017 additional liability due tax rates used in rates
Return issuance period
Tax Cuts and Jobs Act of 2017 Change in Tax Rate Regulatory Liability Return Issuance Period
Tax Cuts and Jobs Act of 2017 Change in Tax Rate Regulatory Liability Return Issuance Period
Disaggregation of Revenue [Table]
Disaggregation of Revenue [Table]
Consolidation Items [Axis]
Consolidation Items [Axis]
Consolidation Items [Domain]
Consolidation Items [Domain]
Operating Segments
Operating Segments [Member]
Product and Service [Axis]
Product and Service [Axis]
Product and Service [Domain]
Product and Service [Domain]
Gas sales revenue [Member]
Gas sales revenue [Member]
Gas sales revenue [Member]
Transportation revenue [Member]
Transportation revenue [Member]
Transportation revenue [Member]
Miscellaneous revenue [Member]
Miscellaneous revenue [Member]
Miscellaneous revenue [Member]
Customer [Axis]
Customer [Axis]
Customer [Domain]
Customer [Domain]
Residential Customers [Member]
Residential Customers [Member]
Residential customers
Commercial Customers [Member]
Commercial Customers [Member]
Commercial customers
Industrial Customers [Member]
Industrial Customers [Member]
Industrial customers
Public Authority and Other Customers [Member]
Public Authority and Other Customers [Member]
Public authority and other customers
Segments [Axis]
Segments [Axis]
Segments [Domain]
Segments [Domain]
Distribution segment
Distribution Segment [Member]
The reportable segment, a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements, comprised of the regulated natural gas distribution and related sales operations.
Pipeline and storage segment
Pipeline and Storage Segment [Member]
The reportable segment, a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements, comprised of the regulated pipeline and storage operations.
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue [Line Items]
Revenue from Contracts with Customer
Revenue from Contract with Customer, Excluding Assessed Tax
Alternative Revenue Program Revenues
Alternative Revenue Program Revenues
Alternative Revenue Program Revenues includes WNA, Weather Normalization Adjustment, which is the program that minimizes the effects of weathers during specific periods of the year.
Other Revenues
Other Revenues
Other operating revenues
Total operating revenues
Revenues
Schedule of Long-term Debt Instruments
Schedule of Long-term Debt Instruments [Table Text Block]
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]
Interim Pension and Other Postretirement Benefit Plan Information
Pension and Other Postretirement Benefits Disclosure [Text Block]
Significant accounting policies
New Accounting Pronouncements, Policy [Policy Text Block]
Regulatory assets and liabilities
Public Utilities, Policy [Policy Text Block]
Earnings Per Share
Earnings Per Share, Policy [Policy Text Block]
Fair Value Measurements
Fair Value Measurement, Policy [Policy Text Block]
Revenue from Contract with Customer
Revenue from Contract with Customer [Policy Text Block]
Revenue Recognition for Alternative Revenue Programs
Revenue Recognition for Alternative Revenue Programs, Policy [Policy Text Block]
Position [Axis]
Position [Axis]
Position [Domain]
Position [Domain]
Long
Long [Member]
Hedging Relationship [Axis]
Hedging Relationship [Axis]
Hedging Relationship [Domain]
Hedging Relationship [Domain]
Cash Flow Hedging
Cash Flow Hedging [Member]
Energy [Axis]
Energy [Axis]
Energy [Domain]
Energy [Domain]
Gas Purchases
Gas Purchases [Member]
Gas Purchases [Member]
Derivative, by Nature [Axis]
Derivative, Name [Domain]
Interest Rate Swap
Interest Rate Swap [Member]
Hedging percent
Derivative, Nonmonetary Notional Amount, Percent of Required Need, Coverage
Energy measure
Derivative, Nonmonetary Notional Amount, Volume
Notional amount
Derivative, Notional Amount
Net realized gain (loss)
Accumulated Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Interest Rate Agreements, Realized Gain (Loss), Net of Tax
Net realized gains and losses in accumulated other comprehensive income from interest rate agreements designated and qualifying as the effective portion of cash flow hedges.
Net gain (loss) on settled interest rate agreements
Interest Rate Cash Flow Hedge Gain (Loss) Reclassified to Earnings, Net
Segment Reporting [Abstract]
Schedule Of Segment Reporting Information By Segment [Table]
Schedule of Segment Reporting Information, by Segment [Table]
Natural Gas, US Regulated
Natural Gas, US Regulated [Member]
Subsegments Consolidation Items [Axis]
Subsegments Consolidation Items [Axis]
Subsegments Consolidation Items [Domain]
Subsegments Consolidation Items [Domain]
Reportable Subsegments
Reportable Subsegments [Member]
Intersubsegment Eliminations
Intersubsegment Eliminations [Member]
Eliminations
Intersegment Eliminations [Member]
Distribution
Pipeline and Storage
Intersegment eliminations
Natural Gas Marketing
Natural Gas Marketing Segment [Member]
Natural Gas Marketing Segment [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information [Line Items]
Segment Reporting Information Profit Loss [Abstract]
Segment Reporting Information, Profit (Loss) [Abstract]
Total operating revenues
Cost of Revenue
Cost of Revenue
Operation and maintenance expense
Other Selling, General and Administrative Expense
Depreciation and amortization expense
Depreciation, Depletion and Amortization, Nonproduction
Taxes, other than income
Taxes, Other
Operating income
Operating Income (Loss)
Other non-operating income (expense)
Other Nonoperating Income (Expense)
Interest charges
Interest Expense
Income before income taxes
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest
Income tax (benefit) expense
Income Tax Expense (Benefit)
Net income
Capital expenditures
Segment Reporting Information, Balance Sheet [Abstract]
Segment Reporting Information, Balance Sheet [Abstract]
-- None. No documentation exists for this element. --
Property, plant and equipment, net
Public Utilities, Property, Plant and Equipment, Net
Total assets
Assets
Schedule of Segment Reporting Information, by Segment
Schedule of Segment Reporting Information, by Segment [Table Text Block]
Cummulative effect on accounting change, on equity or net assets
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets
Regulatory Assets and Liabilities Disclosure [Abstract]
Schedule Of Regulatory Assets [Table]
Schedule of Regulatory Assets [Table]
Regulatory Asset [Axis]
Regulatory Asset [Axis]
Regulatory Asset [Domain]
Regulatory Asset [Domain]
Pension and other postreitrement plans costs
Pension and Other Postretirement Plans Costs [Member]
Infrastructure mechanisms
Infrastructure Mechanisms [Member]
Costs associated with capital expenditures incurred pursuant to the risk-based program for the renewal or replacement of distribution facilities, including steel service lines, that would otherwise be charged to expense. These costs are included in allowable costs for rate making purposes and future revenue will be provided to permit recovery of such incurred costs.
Deferred gas costs
Deferred Fuel Costs [Member]
Recoverable loss on reacquired debt
Loss on Reacquired Debt [Member]
Deferred pipeline record collection costs
Deferred Project Costs [Member]
Rate case costs
Rate Case Costs [Member]
Costs incurred during the rate making process that would otherwise be charged to expense. These costs are included in allowable costs for rate making purposes and future revenue will be provided to permit recovery of such incurred costs.
Other
Other Regulatory Assets (Liabilities) [Member]
Regulatory Asset [Line Items]
Regulatory Assets [Line Items]
Regulatory assets
Regulatory Assets
Schedule Of Regulatory Liabilities [Table]
Schedule of Regulatory Liabilities [Table]
Regulatory excess deferred taxes
Deferred Income Tax Charge [Member]
Regulatory cost of removal obligation
Removal Costs [Member]
Asset retirement obligation
Asset Retirement Obligation Costs [Member]
APT annual adjustment mechanism
Regulatory Clause Revenues Over Recovered [Member]
Regulatory Clause Revenues Over Recovered [Member]
Regulatory Liabilities [Line Items]
Regulatory Liabilities [Line Items]
Regulatory liabilities
Regulatory Liabilities
Basic and Diluted Earnings Per Share, Continuing Operations [Abstract]
Basic and Diluted Earnings Per Share, Continuing Operations [Abstract]
Basic and Diluted Earnings Per Share, Continuing Operations [Abstract]
Net Income
Income allocated to participating securities
Undistributed Earnings (Loss) Allocated to Participating Securities, Basic
Income available to common shareholders
Net Income (Loss) Available to Common Stockholders, Basic
Basic weighted average shares outstanding
Weighted Average Number of Shares Outstanding, Basic
Basic net income per share
Earnings Per Share, Basic
Effect of dilutive shares
Dilutive Securities, Effect on Basic Earnings Per Share, Options and Restrictive Stock Units
Income available to common shareholders
Net Income (Loss) Available to Common Stockholders, Diluted
Additional dilutive shares
Incremental Common Shares Attributable to Dilutive Effect of Equity Forward Agreements
Diluted weighted average shares outstanding
Weighted Average Number of Shares Outstanding, Diluted
Diluted net income per share
Earnings Per Share, Diluted
Statement of Stockholders' Equity [Abstract]
Statement [Table]
Statement [Table]
Equity Components [Axis]
Equity Components [Axis]
Equity Component [Domain]
Equity Component [Domain]
Common Stock [Member]
Common Stock [Member]
Additional Paid-in Capital [Member]
Additional Paid-in Capital [Member]
Accumulated Other Comprehensive Income
AOCI Attributable to Parent [Member]
Retained Earnings [Member]
Retained Earnings [Member]
Statement [Line Items]
Statement [Line Items]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shareholders' equity, beginning balance
Stockholders' Equity Attributable to Parent
Other Comprehensive Loss, Net of Tax
Other Comprehensive Income (Loss), Net of Tax
Cash dividends
Dividends, Common Stock, Cash
Cumulative Effect of New Accounting Principle in Period of Adoption
Cumulative Effect of New Accounting Principle in Period of Adoption
Stock Issued or Granted During Period, Share-based Compensation [Abstract]
Stock Issued or Granted During Period, Share-based Compensation [Abstract]
Public and other stock offerings (in shares)
Stock Issued During Period, Shares, New Issues
Public and other stock offerings
Stock Issued During Period, Value, New Issues
Stock-based compensation plans (in shares)
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures
Stock-based compensation plans
Stock Issued During Period, Value, Share-based Compensation, Net of Forfeitures
Shareholders' equity, ending balance
Cash dividends per share
Common Stock, Dividends, Per Share, Cash Paid
Impact of the Tax Cuts and Jobs Act of 2017
Income Tax Disclosure [Text Block]
Long-term Debt, Fair Value
Long-term Debt, Fair Value
Income Statement [Abstract]
Operating revenues
Revenues [Abstract]
Operating income
Income before income taxes
Income tax expense
Other comprehensive income (loss), net of tax
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract]
Net unrealized holding gains (losses) on available-for-sale securities, net of tax
Other Comprehensive Income (Loss), Securities, Available-for-sale, Adjustment, after Tax
Cash flow hedges:
Cash Flow Hedges [Abstract]
Cash Flow Hedges [Abstract]
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax
Total other comprehensive income (loss)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent
Total comprehensive income
Comprehensive Income (Loss), Net of Tax, Attributable to Parent
Increase (decrease) in fair value:
Interest Rate Fair Value Hedges [Abstract]
Interest rate agreements
Other Comprehensive Income, Unrealized Gain (Loss) On Interest Rate Agreements Arising During Period, Net Of Tax
Change in accumulated gains and losses from interest rate agreements designated and qualifying as the effective portion of cash flow hedges, net of tax effect. The after tax effect change includes an entity's share of an equity investee's Increase or Decrease in deferred hedging gains or losses.
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Interest rate agreements
Other Comprehensive Income, Reclassification Adjustment On Interest Rate Agreements Included In Net Income, Net Of Tax
Net of tax effect of the reclassification adjustment for accumulated gains and losses from interest rate agreements designated and qualifying as the effective portion of cash flow hedges included in accumulated comprehensive income that was realized in net income during the period.
Total other comprehensive income (loss) from hedging, net of tax
Line Of Credit Facility [Abstract]
Line of Credit Facility [Abstract]
Line Of Credit Facility [Table]
Line of Credit Facility [Table]
Variable Rate [Axis]
Variable Rate [Axis]
Variable Rate [Domain]
Variable Rate [Domain]
LIBOR
London Interbank Offered Rate (LIBOR) [Member]
Five Year Unsecured Revolving Credit Agreement
Five Year Unsecured Revolving Credit Agreement [Member]
Regulated Operations Five Year Unsecured Revolving Credit Agreement
$25 Million Bank Loan Agreement
$25 Million Bank Loan Agreement [Member]
Regulated Operations $25 million Loan Agreement with Amarillo National Bank.
$10 Million Revolving Credit Note
$10 Million Revolving Credit Note [Member]
Regulated Operations $10 million Revolving Credit Note with the Bank of Texas.
Credit Facility [Axis]
Credit Facility [Axis]
Credit Facility [Domain]
Credit Facility [Domain]
Commercial Paper
Commercial Paper [Member]
Revolving Credit Facility
Revolving Credit Facility [Member]
Line of Credit
Line of Credit [Member]
Line Of Credit Facility [Line Items]
Line of Credit Facility [Line Items]
Proceeds from Issuance of Debt
Proceeds from Issuance of Debt
Effective interest rate
Debt Instrument, Interest Rate, Effective Percentage
Equity-to-total-capitalization ratio
Public Utilities, Approved Equity Capital Structure, Percentage
Maximum borrowing capacity
Line of Credit Facility, Maximum Borrowing Capacity
Interest rate spread
Debt Instrument, Basis Spread on Variable Rate
Accordion feature
Line of Credit Facility, Accordion Feature
Monetary value of the accordion feature, the additional line of credit portion that could be borrowed against with the approval of the issuing banks.
Maximum borrowing capacity post accordion feature
Line of Credit Facility, Maximum Borrowing Capacity with Accordion Feature
Maximum available borrowing capacity under the credit facility with consideration of any additional commited line portions under the accordion feature that could be borrowed against with the approval of the issuing banks.
Outstanding commercial paper
Commercial Paper
Outstanding borrowings
Long-term Line of Credit
Remaining borrowing capacity
Line of Credit Facility, Remaining Borrowing Capacity
Maximum debt-to-total-capitalization ratio
Public Utilities, Approved Debt Capital Structure, Percentage
Debt-to-total-capitalization ratio
Public Utilities, Actual Debt Capital Structure, Percentage
Public Utilities, Actual Debt Capital Structure, Percentage
Outstanding indebtedness
Debt Instrument, Covenant Compliance, Default Provision, Indebtedness Threshold
Debt Instrument, Covenant Compliance, Default Provision Trigger Amount
ASSETS
Assets [Abstract]
Property, plant and equipment
Public Utilities, Property, Plant and Equipment, Plant in Service
Less accumulated depreciation and amortization
Public Utilities, Property, Plant and Equipment, Accumulated Depreciation
Net property, plant and equipment
Current assets
Assets, Current [Abstract]
Cash and cash equivalents
Accounts receivable, net
Accounts Receivable, Net, Current
Gas stored underground
Energy Related Inventory, Gas Stored Underground
Other current assets
Other Assets, Current
Total current assets
Assets, Current
Goodwill
Goodwill
Deferred charges and other assets
Other Assets, Noncurrent
Total assets
CAPITALIZATION AND LIABILITIES
Liabilities and Equity [Abstract]
Shareholders’ equity
Stockholders' Equity Attributable to Parent [Abstract]
Common stock, no par value (stated at $0.005 per share)
Common Stock, Value, Issued
Additional paid-in capital
Additional Paid in Capital, Common Stock
Accumulated other comprehensive loss
Accumulated Other Comprehensive Income (Loss), Net of Tax
Retained earnings
Retained Earnings (Accumulated Deficit)
Shareholders’ equity
Total capitalization
Capitalization, Long-term Debt and Equity
Current liabilities
Liabilities, Current [Abstract]
Accounts payable and accrued liabilities
Accounts Payable and Accrued Liabilities, Current
Other current liabilities
Other Liabilities, Current
Short-term debt
Short-term Debt
Current maturities of long-term debt
Total current liabilities
Liabilities, Current
Deferred income taxes
Deferred Tax Liabilities, Net, Noncurrent
Regulatory excess deferred taxes (See Note 13)
Tax Cuts and Jobs Act of 2017, Change in Tax Rate, Deferred Tax Liability
Tax Cuts and Jobs Act of 2017, Change in Tax Rate, Deferred Tax Liability
Regulatory Cost Of Removal Liability Noncurrent
Regulatory Cost Of Removal Liability Noncurrent
Regulatory Cost Of Removal Liability Noncurrent
Pension and postretirement liabilities
Liability, Defined Benefit Plan, Noncurrent
Deferred credits and other liabilities
Other Liabilities, Noncurrent
Total shareholders' equity and liabilities
Liabilities and Equity
Loss Contingency [Abstract]
Loss Contingency [Abstract]
Loss Contingencies [Table]
Loss Contingencies [Table]
Litigation Case [Axis]
Litigation Case [Axis]
Litigation Case [Domain]
Litigation Case [Domain]
Civil Action, Dallas, Texas
Civil Action Dallas Texas [Member]
Civil Action Dallas Texas [Member]
Loss Contingencies [Line Items]
Loss Contingencies [Line Items]
Self-insurance retention expense
Self Insured Retention Expense
Self Insured Retention Expense
Damages sought
Loss Contingency, Damages Sought, Value
Leases [Abstract]
Leases [Abstract]
Schedule of Operating Leased Assets [Table]
Schedule of Operating Leased Assets [Table]
Operating Leased Assets [Line Items]
Operating Leased Assets [Line Items]
Operating leases, future minimum payments due
Operating Leases, Future Minimum Payments Due
Lease term of contract
Lessee, Operating Lease, Term of Contract
Debt
Debt Disclosure [Text Block]
Schedule of Available For Sale Securities [Abstract]
Debt Securities, Available-for-sale [Abstract]
Schedule of Available for Sale Securities [Table]
Schedule of Available-for-sale Securities [Table]
Domestic equity mutual funds(1)
Equity Funds Domestic [Member]
An investment that pools funds from many investors to invest in a combination of underlying domestic investments, primarily equity investments.
Foreign equity mutual funds(1)
Equity Funds Foreign [Member]
An investment that pools funds from many investors to invest in a combination of underlying foreign investments, primarily equity investments.
Schedule Of Available For Sale Securities [Line Items]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost
Available-for-sale Securities, Amortized Cost Basis
Schedule of Stock by Class [Table]
Schedule of Stock by Class [Table]
Sale of Stock [Axis]
Sale of Stock [Axis]
Sale of Stock [Domain]
Sale of Stock [Domain]
Shelf Registration Statement
Shelf Registration Statement [Member]
Shelf Registration Statement [Member]
At-The-Market
At-The-Market [Member]
At-The-Market [Member]
Common Stock Block Trade
Common Stock Block Trade [Member]
Common Stock Block Trade [Member]
Forward Contract Indexed to Issuer's Equity, Type [Axis]
Forward Contract Indexed to Issuer's Equity, Type [Axis]
Forward Contract Indexed to Issuer's Equity, Type [Domain]
Forward Contract Indexed to Issuer's Equity, Type [Domain]
Forward Sales Equity Agreement, November 2018
Forward Sales Equity, November [Member]
Total forward sale agreement details for the two underwriters who borrowed and sold shares of our common stock in November 2018.
Forward Sales Equity Agreement, February 2019
Forward Sales Equity Agreement, February 2019 [Member]
Total forward sale agreement details for the various underwriters who borrowed and sold shares of our common stock in February 2019.
Class of Stock [Line Items]
Class of Stock [Line Items]
Debt and equity securities authorized for issuance
Debt and Equity Securities Authorized for Issuance
The total dollar amount of debt and equity securities authorized to be issued.
Debt and equity securities authorized for issuance value remaining
Debt And Equity Securities Available For Issuance
The total dollar amount of debt and equity securities available to be issued.
Value of shares authorized for issuance
Sale of Stock, Value of Shares Authorized
Sale of Stock, Value of Shares Authorized
Value of shares available for issuance
Sale of Stock Value of Shares Available for Issuance
Value of shares remaining available for issuance
Stock Issued During Period, New Issues (in shares)
Gross proceeds from equity offering
Proceeds from issuance of common stock gross
Proceeds from issuance of common stock gross
Forward sales equity agreement, shares
Forward Contract Indexed to Issuer's Equity, Shares
Forward sales equity agreement, settlement date
Forward Contract Indexed to Issuer's Equity, Settlement Date
Forward sales equity agreement, settlements
Forward sales equity agreement, settlements
Forward sales equity agreement, settlements
Forward sales equity agreement, settlement alternatives, cash, at fair value
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Cash, at Fair Value
Forward sales equity agreement, forward rate per share
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share
Revenue Disclosure [Abstract]
Revenue Disclosure [Abstract]
Alternative Revenue Program [Table]
Alternative Revenue Program [Table]
Alternative Revenue Program [Table]
Alternative Revenue Program [Line Items]
Alternative Revenue Program [Line Items]
[Line Items] for Alternative Revenue Program [Table]
Rate Case Revenue Benchmark
Rate Case Revenue Benchmark
Rate case revenue benchmark as set in the APT rate case filing and part of our regulatory mechanism. This revenue benchmark is used in calculating the total revenue to be billed or returned to customers.
Regulatory Mechanism Threshold
Regulatory Mechanism Threshold
APT has a regulatory mechanism that requires that we share with its tariffed customers a set percentage, as determined through the rate case filings, of the difference between the total non-tariffed revenues earned during a test period and a revenue benchmark.
Shareholders' Equity and Accumulated Other Comprehensive Income
Stockholders' Equity Note Disclosure [Text Block]
Unaudited Financial Information
Significant Accounting Policies [Text Block]
Document And Entity Information [Abstract]
-- None. No documentation exists for this element. --
Entity Registrant Name
Entity Central Index Key
Current Fiscal Year End Date
Entity Filer Category
Document Type
Document Period End Date
Document Fiscal Year Focus
Document Fiscal Period Focus
Amendment Flag
Entity Common Stock, Shares Outstanding
Entity Small Business
Entity Small Business
Entity Emerging Growth Company
Entity Emerging Growth Company
Schedule of Defined Benefit Plans Disclosures [Table]
Schedule of Defined Benefit Plans Disclosures [Table]
Retirement Plan Type [Axis]
Retirement Plan Type [Axis]
Retirement Plan Type [Domain]
Retirement Plan Type [Domain]
Pension Benefits
Pension Plan [Member]
Other Benefits
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Disclosure [Line Items]
Service cost
Defined Benefit Plan, Service Cost
Interest cost
Defined Benefit Plan, Interest Cost
Expected return on assets
Defined Benefit Plan, Expected Return (Loss) on Plan Assets
Amortization of prior service cost (credit)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)
Amortization of actuarial (gain) loss
Defined Benefit Plan, Amortization of Gain (Loss)
Settlements
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement
Net periodic pension cost
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Net unrealized holding gains (losses) on available-for-sale securities, tax
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax
Amortization and unrealized gain (loss) on interest rate agreements, tax
Other Comprehensive Income (Loss), Interest Rate Contract, Derivatives Qualifying as Hedges, Tax
Other Comprehensive Income (Loss), Interest Rate Contract, Derivatives Qualifying as Hedges, Tax
Segment Information
Segment Reporting Disclosure [Text Block]
Accumulated Other Comprehensive Income (Loss) [Table]
Accumulated Other Comprehensive Income (Loss) [Table]
Available- for-Sale Securities(1)
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
Cash Flow Hedges
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss) [Line Items]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss) before reclassifications
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax
Amounts reclassified from accumulated other comprehensive income
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax
Net current-period other comprehensive income (loss)
Earnings Per Share
Earnings Per Share [Text Block]