XML 200 R48.htm IDEA: XBRL DOCUMENT v3.10.0.1
EMPLOYEE BENEFIT PLANS (Details) - USD ($)
3 Months Ended 9 Months Ended 12 Months Ended
Dec. 31, 2016
Sep. 30, 2016
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]          
Regulatory Assets, Noncurrent     $ 437,479,000 $ 405,189,000  
Defined Benefit Plan, Benefit Obligation, Payment for Settlement       $ 46,700,000  
Defined Benefit Plan Assumptions Used To Determine Benefit Obligations Rate of Compensation Increase, Minimum     3.20% 3.25%  
Defined Benefit Plan Assumptions Used To Determine Benefit Obligations Rate of Compensation Increase, Maximum     4.00% 3.35%  
Compensation increase rate - minimum     3.25% 3.25% 3.35%
Compensation increase rate- maximum     3.35% 3.40% 3.40%
Description of basis used to determine overall expected long-term rate of return on plan assets     We determine our overall expected long-term rate of return on plan assets, based on our review of historical returns and economic growth models. As of December 31, 2014, we updated our assumed mortality rates to incorporate the new set of mortality tables issued by the Society of Actuaries in October 2014. We determine our discount rates annually.  We estimate our discount rate based upon a comparison of the expected cash flows associated with our future payments under our defined benefit pension and other postemployment obligations to a hypothetical bond portfolio created using high-quality bonds that closely match expected cash flows.  Bond portfolios are developed by selecting a bond for each of the next 60 years based on the maturity dates of the bonds.  Bonds selected to be included in the portfolios are only those rated by Moody’s as AA- or better and exclude callable bonds, bonds with less than a minimum issue size, yield outliers and other filtering criteria to remove unsuitable bonds.    
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Noncurrent liabilities     $ (178,720,000) $ (172,938,000)  
Assets expected to be withdrawn or returned     0    
Amortization of unrecognized prior service cost     (4,567,000) (4,597,000) $ (3,316,000)
Defined Benefit Plan, Amortization of Gain (Loss)     (43,800,000) (42,591,000) (40,912,000)
Total recognized in other comprehensive income (loss)     1,407,000 $ (778,000) (314,000)
Amount recognized in other comprehensive income     $ 0    
Health care cost-trend rate assumed for next year     7.00% 7.00%  
Rate to which the cost-trend rate is assumed to decline (the ultimate trend rate)     5.00% 5.00%  
Year that the rate reaches the ultimate trend rate     2024 2023  
Target asset allocation     100.00%    
US Large-Cap Equity [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Target asset allocation     18.00%    
Investment-grade bonds [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Target asset allocation     40.00%    
Developed foreign large-cap equities [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Target asset allocation     10.00%    
Alternative investments [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Target asset allocation     14.00%    
Mid-cap equities [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Target asset allocation     7.00%    
Emerging market equities [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Target asset allocation     6.00%    
Small-cap equities [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Target asset allocation     5.00%    
Equity Securities [Member]          
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]          
Defined Benefit Plan, Plan Assets, Investment Policy and Strategy, Description     0.7    
Fixed Income Funds [Member]          
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]          
Defined Benefit Plan, Plan Assets, Investment Policy and Strategy, Description     0.3    
Pension Plan [Member]          
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]          
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant     $ 0 $ 0  
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant     0 0  
Net periodic benefit cost     29,054,000 30,240,000 $ 31,965,000
Plan amendment     $ 0 $ 0  
Discount rate     4.40% 3.80%  
Weighted average discount rate     3.80% 4.30% 4.75%
Expected long-term return on plan assets     7.25% 7.75% 7.75%
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]          
Benefit obligation, beginning of period     $ 993,891,000 $ 966,531,000  
Service cost     12,919,000 12,176,000 $ 12,055,000
Interest cost     36,801,000 40,453,000 45,550,000
Actuarial loss (gain)     (42,540,000) 76,325,000  
Plan amendment     0 0  
Benefits paid     (50,561,000) (55,107,000)  
Settlements     0 46,487,000  
Benefit obligation, end of period $ 966,531,000   950,510,000 993,891,000 966,531,000
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Actual return on plan assets     (62,752,000) 135,056,000  
Employer contributions     42,386,000 111,936,000  
Settlements     235,000 46,667,000  
Fair value of plan assets, end of period 739,586,000   814,112,000 884,804,000 739,586,000
Balance at December 31     (136,398,000) (109,087,000)  
Current liabilities     (962,000) (963,000)  
Noncurrent liabilities     (135,436,000) (108,124,000)  
Balance at December 31     (136,398,000) (109,087,000)  
Accumulated benefit obligation     890,400,000 936,700,000  
Service cost     12,919,000 12,176,000 12,055,000
Interest cost     36,801,000 40,453,000 45,550,000
Expected return on assets     (60,579,000) (58,496,000) (61,183,000)
Amortization of unrecognized prior service cost     1,082,000 837,000 751,000
Defined Benefit Plan, Amortization of Gain (Loss)     (39,913,000) (36,107,000) (35,543,000)
Net loss arising during the period     1,173,000 (2,101,000) (1,262,000)
Deferred income taxes     (848,000) 486,000 197,000
Total recognized in other comprehensive income (loss)     (1,407,000) 778,000 314,000
Accumulated loss     (419,238,000) (378,595,000)  
Accumulated other comprehensive loss before regulatory assets     (419,238,000) (378,595,000)  
Regulatory asset for regulated entities     412,545,000 369,647,000  
Accumulated other comprehensive loss after regulatory assets     (6,693,000) (8,948,000)  
Deferred income taxes     2,607,000 3,455,000  
Accumulated other comprehensive loss, net of tax     (4,086,000) (5,493,000)  
Prior service credit (cost) expected to be recognized in following fiscal year     0    
Actuarial net loss, to be recognized in 2017     33,039,000    
Effect of a one percentage point change on total of service and interest cost - increase     200,000    
Effect of a one percentage point change on other postemployment benefit obligation - increase     2,300,000    
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]          
Level 3 fair value measurement, January 1     113,865,000 102,492,000  
Net realized and unrealized gains (losses)     (115,000) 7,624,000  
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases     0 16,300,000  
Settlements     (4,100,000) (12,551,000)  
Level 3 fair value measurement, December 31 102,492,000   109,650,000 113,865,000 102,492,000
Employer contributions     42,386,000 111,936,000  
Expected employer contributions in 2017     1,000,000    
2017     52,368,000    
2018     53,332,000    
2019     54,245,000    
2020     55,474,000    
2021     56,477,000    
2022 through 2027     295,565,000    
Defined Benefit Plan, Benefit Obligation, Benefits Paid     50,561,000 55,107,000  
Pension Plan [Member] | Equity Securities [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     318,538,000 392,925,000  
Pension Plan [Member] | Government Obligations [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     69,475,000 74,596,000  
Pension Plan [Member] | Corporate Obligations [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     240,900,000 260,907,000  
Pension Plan [Member] | Cash and Money Market Funds [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     74,410,000 41,926,000  
Pension Plan [Member] | Insurance contracts and group annuity contracts [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     30,445,000 35,158,000  
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]          
Level 3 fair value measurement, January 1     35,158,000 45,140,000  
Net realized and unrealized gains (losses)     (611,000) 2,569,000  
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases     0 0  
Settlements     (4,100,000) (12,551,000)  
Level 3 fair value measurement, December 31 45,140,000   30,445,000 35,158,000 45,140,000
Pension Plan [Member] | Other Investments [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     80,344,000 79,292,000  
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]          
Level 3 fair value measurement, January 1     78,707,000 57,352,000  
Net realized and unrealized gains (losses)     496,000 5,055,000  
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases     0 16,300,000  
Settlements     0 0  
Level 3 fair value measurement, December 31 $ 57,352,000   79,205,000 78,707,000 57,352,000
Pension Plan [Member] | Level 1 [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     285,087,000 323,050,000  
Pension Plan [Member] | Level 1 [Member] | Equity Securities [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     282,668,000 301,911,000  
Pension Plan [Member] | Level 1 [Member] | Government Obligations [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     0 0  
Pension Plan [Member] | Level 1 [Member] | Corporate Obligations [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     0 0  
Pension Plan [Member] | Level 1 [Member] | Cash and Money Market Funds [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     2,419,000 21,139,000  
Pension Plan [Member] | Level 1 [Member] | Insurance contracts and group annuity contracts [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     0 0  
Pension Plan [Member] | Level 1 [Member] | Other Investments [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     0 0  
Pension Plan [Member] | Level 2 [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     419,375,000 447,889,000  
Pension Plan [Member] | Level 2 [Member] | Equity Securities [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     35,870,000 91,014,000  
Pension Plan [Member] | Level 2 [Member] | Government Obligations [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     69,475,000 74,596,000  
Pension Plan [Member] | Level 2 [Member] | Corporate Obligations [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     240,900,000 260,907,000  
Pension Plan [Member] | Level 2 [Member] | Cash and Money Market Funds [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     71,991,000 20,787,000  
Pension Plan [Member] | Level 2 [Member] | Insurance contracts and group annuity contracts [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     0 0  
Pension Plan [Member] | Level 2 [Member] | Other Investments [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     1,139,000 585,000  
Pension Plan [Member] | Level 3 [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     109,650,000 113,865,000  
Pension Plan [Member] | Level 3 [Member] | Equity Securities [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     0 0  
Pension Plan [Member] | Level 3 [Member] | Government Obligations [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     0 0  
Pension Plan [Member] | Level 3 [Member] | Corporate Obligations [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     0 0  
Pension Plan [Member] | Level 3 [Member] | Cash and Money Market Funds [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     0 0  
Pension Plan [Member] | Level 3 [Member] | Insurance contracts and group annuity contracts [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period       35,158,000  
Pension Plan [Member] | Level 3 [Member] | Other Investments [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period       78,707,000  
Other Postretirement Benefits Plan [Member]          
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]          
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant     3,563,000 3,483,000  
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant     3,563,000 3,483,000  
Net periodic benefit cost     $ (3,493,000) 1,696,000 2,593,000
Minimum number of years of service for certain employees to be eligible to participate in shared welfare plans that provide postemployment medical and life insurance benefits     5    
Plan amendment     $ 0 $ (171,000)  
Discount rate     4.40% 3.70%  
Weighted average discount rate 3.75% 4.75% 3.70% 4.20%  
Expected long-term return on plan assets 7.75% 8.00% 7.60% 7.60%  
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]          
Benefit obligation, beginning of period     $ 255,040,000 $ 243,548,000  
Service cost     2,354,000 2,509,000 2,675,000
Interest cost     9,117,000 9,890,000 10,235,000
Actuarial loss (gain)     (31,607,000) 12,129,000  
Plan amendment     0 (171,000)  
Benefits paid     (18,323,000) (16,690,000)  
Settlements     0 0  
Benefit obligation, end of period $ 243,548,000   220,144,000 255,040,000 243,548,000
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Actual return on plan assets     (6,325,000) 31,228,000  
Employer contributions     7,718,000 6,159,000  
Settlements     0 0  
Fair value of plan assets, end of period $ 166,046,000   176,859,000 190,226,000 166,046,000
Balance at December 31     (43,285,000) (64,814,000)  
Current liabilities     0 0  
Noncurrent liabilities     (43,285,000) (64,814,000)  
Balance at December 31     (43,285,000) (64,814,000)  
Service cost     2,354,000 2,509,000 2,675,000
Interest cost     9,117,000 9,890,000 10,235,000
Expected return on assets     (14,284,000) (12,590,000) (12,370,000)
Amortization of unrecognized prior service cost     (4,567,000) (4,597,000) (3,316,000)
Defined Benefit Plan, Amortization of Gain (Loss)     (3,887,000) (6,484,000) (5,369,000)
Prior service credit (cost)     875,000 5,442,000  
Accumulated loss     (34,144,000) (49,030,000)  
Accumulated other comprehensive loss before regulatory assets     (33,269,000) (43,588,000)  
Regulatory asset for regulated entities     33,269,000 43,588,000  
Accumulated other comprehensive loss after regulatory assets     0 0  
Prior service credit (cost) expected to be recognized in following fiscal year     (673,000)    
Actuarial net loss, to be recognized in 2017     2,244,000    
Effect of a one percentage point change on total of service and interest cost - decrease     (200,000)    
Effect of a one percentage point change on other postemployment benefit obligation - decrease     (2,400,000)    
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]          
Employer contributions     7,718,000 6,159,000  
Expected employer contributions in 2017     3,000,000    
2017     16,746,000    
2018     16,737,000    
2019     16,632,000    
2020     16,603,000    
2021     16,424,000    
2022 through 2027     77,769,000    
Defined Benefit Plan, Benefit Obligation, Benefits Paid     18,323,000 16,690,000  
Other Postretirement Benefits Plan [Member] | Equity Securities [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     60,469,000 63,303,000  
Other Postretirement Benefits Plan [Member] | Government Obligations [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     74,000 101,000  
Other Postretirement Benefits Plan [Member] | Corporate Obligations [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     25,857,000 25,905,000  
Other Postretirement Benefits Plan [Member] | Cash and Money Market Funds [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     1,549,000 4,540,000  
Other Postretirement Benefits Plan [Member] | Insurance contracts and group annuity contracts [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     88,910,000 96,377,000  
Other Postretirement Benefits Plan [Member] | Level 1 [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     59,336,000 67,692,000  
Other Postretirement Benefits Plan [Member] | Level 1 [Member] | Equity Securities [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     58,087,000 63,180,000  
Other Postretirement Benefits Plan [Member] | Level 1 [Member] | Government Obligations [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     0 0  
Other Postretirement Benefits Plan [Member] | Level 1 [Member] | Corporate Obligations [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     0 0  
Other Postretirement Benefits Plan [Member] | Level 1 [Member] | Cash and Money Market Funds [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     1,249,000 4,512,000  
Other Postretirement Benefits Plan [Member] | Level 1 [Member] | Insurance contracts and group annuity contracts [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     0 0  
Other Postretirement Benefits Plan [Member] | Level 2 [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     117,523,000 122,534,000  
Other Postretirement Benefits Plan [Member] | Level 2 [Member] | Equity Securities [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     2,382,000 123,000  
Other Postretirement Benefits Plan [Member] | Level 2 [Member] | Government Obligations [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     74,000 101,000  
Other Postretirement Benefits Plan [Member] | Level 2 [Member] | Corporate Obligations [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     25,857,000 25,905,000  
Other Postretirement Benefits Plan [Member] | Level 2 [Member] | Cash and Money Market Funds [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     300,000 28,000  
Other Postretirement Benefits Plan [Member] | Level 2 [Member] | Insurance contracts and group annuity contracts [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     88,910,000 96,377,000  
Other Postretirement Benefits Plan [Member] | Level 3 [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     0 0  
Other Postretirement Benefits Plan [Member] | Level 3 [Member] | Equity Securities [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     0 0  
Other Postretirement Benefits Plan [Member] | Level 3 [Member] | Government Obligations [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     0 0  
Other Postretirement Benefits Plan [Member] | Level 3 [Member] | Corporate Obligations [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     0 0  
Other Postretirement Benefits Plan [Member] | Level 3 [Member] | Cash and Money Market Funds [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     0 0  
Other Postretirement Benefits Plan [Member] | Level 3 [Member] | Insurance contracts and group annuity contracts [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]          
Fair value of plan assets, end of period     $ 0 0  
ONE Gas 401(k) Plan [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]          
Percent of employee contributions matched of eligible compensation (in hundredths)     100.00%    
Maximum percentage of each participants eligible compensation subject to certain limits matching (in hundredths)     6.00%    
Contributions made to 401(k) plan     $ 12,100,000 11,700,000 10,800,000
ONE Gas Profit-Sharing Plan [Member]          
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]          
Profit sharing contribution percentage     1.00%    
Contributions made to profit-sharing plan     $ 7,400,000 $ 8,100,000 $ 6,000,000
Non-service Costs [Member]          
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]          
Regulatory Assets, Noncurrent     $ 1,500,000