CREDIT FACILITIES (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Line of Credit Facility [Line Items]
Ratio of Indebtedness to Net Capital	0.4
Commercial paper maximum borrowing capacity	$ 700,000,000
Commercial Paper	0	42,000,000
Letters of Credit Outstanding, Amount	1,000,000
Line of Credit Facility, Remaining Borrowing Capacity	699,000,000
Line of Credit [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Covenant Description	The ONE Gas Credit Agreement contains certain financial, operational and legal covenants. Among other things, these covenants include maintaining ONE Gas’ debt-to-capital ratio of no more than 70 percent at the end of any calendar quarter. The ONE Gas Credit Agreement also contains customary affirmative and negative covenants, including covenants relating to liens, indebtedness of subsidiaries, investments, changes in the nature of business, fundamental changes, transactions with affiliates, burdensome agreements and use of proceeds. In the event of a breach of certain covenants by ONE Gas, amounts outstanding under the ONE Gas Credit Agreement may become due and payable immediately.
Line of Credit Facility, Interest Rate Description	Borrowings, if any, will accrue interest at LIBOR plus 79.5 basis points.
Line of credit facility sublimit	50,000,000
Line Of Credit Facility Option To Increase Borrowing Capacity	1,200,000,000
Line of Credit Facility, Maximum Borrowing Capacity	$ 700,000,000
Line of Credit Facility, Commitment Fee Description	The annual facility fee is 8 basis points.