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EMPLOYEE BENEFIT PLANS (Details) (USD $)
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1 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended |
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Jan. 31, 2014
ONE Gas Pension and Postretirement Benefit Plans [Member]
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Sep. 30, 2013
ONE Gas Pension and Postretirement Benefit Plans [Member]
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Sep. 30, 2013
ONE Gas Pension and Postretirement Benefit Plans [Member]
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Sep. 30, 2014
ONE Gas Pension Plans [Member]
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Sep. 30, 2014
ONE Gas Pension Plans [Member]
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Sep. 30, 2014
ONE Gas Postretirement Benefit Plans [Member]
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Sep. 30, 2014
ONE Gas Postretirement Benefit Plans [Member]
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| Employee Benefit Plans [Line Items] | |||||||
| Benefit obligation transferred from ONEOK | $ 1,100,000,000 | ||||||
| Fair value of plan assets transferred from ONEOK | 1,000,000,000 | ||||||
| Increase in regulatory assets as a result of the transfer of unrecognized losses from ONEOK | 331,000,000 | ||||||
| Increase in deferred income taxes as a result of the transfer of unrecognized losses from ONEOK | 86,000,000 | ||||||
| Components of net periodic benefit cost: | |||||||
| Service cost | 3,554,000 | 9,227,000 | 867,000 | 2,908,000 | |||
| Interest cost | 10,948,000 | 32,844,000 | 2,901,000 | 8,703,000 | |||
| Expected return on assets | (14,965,000) | (44,895,000) | (2,848,000) | (8,544,000) | |||
| Amortization of unrecognized prior service cost | 137,000 | 411,000 | (440,000) | (1,320,000) | |||
| Amortization of net loss | 7,550,000 | 22,649,000 | 992,000 | 2,976,000 | |||
| Net periodic benefit cost | $ 13,400,000 | $ 40,600,000 | $ 7,224,000 | $ 20,236,000 | $ 1,472,000 | $ 4,723,000 |