SEPARATION & RELATED-PARTY TRANSACTIONS (Details) (USD $)	1 Months Ended	12 Months Ended
	Jan. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014
Separation & Related Party Transaction [Line Items]
Proceeds from Issuance of Private Placement	$ 1,190,000,000
Cash Payment to ONEOK Upon Separation	1,130,000,000
Common Stock, Shares Authorized	250,000,000	1,000		250,000,000
Preferred Stock, Shares Authorized	50,000,000			50,000,000
Operations and maintenance [Abstract]
Accounts Receivable, Related Parties				0
Long-term line of credit with ONEOK		1,027,631,000		0
Plant, property and equipment, net	21,459,000
Regulatory assets, pension and other post-retirements benefits	331,148,000
Other assets transferred	80,700,000
Long-term line of credit with ONEOK	1,027,631,000
Short-term note payable to ONEOK	397,857,000
Pension and other postretirement benefits - liabilities	(123,800,000)
Other liabilities transferred	(34,404,000)
Deferred taxes	(86,112,000)
Accumulated other comprehensive loss	(3,393,000)
Net contribution of assets (liabilities)	1,611,086,000
Less: Cash paid to ONEOK	1,130,000,000
Net transfers from ONEOK upon separation	481,086,000
ONEOK, Inc. [Member]
Separation & Related Party Transaction [Line Items]
Total share-based compensation cost charged to us by ONEOK		15,500,000	12,400,000
Pension and postretirement health and life insurance plans costs charged to us by ONEOK, net		52,100,000	43,400,000
Amount of pension and postretirement health and life insurance costs deferred through regulatory mechanisms		1,800,000	4,100,000
Expense [Abstract]
Cost of natural gas		226,582,000	135,650,000
Operations and maintenance [Abstract]
Direct employee labor and benefits costs		177,526,000	165,798,000
Allocated employee labor and benefit costs		29,955,000	24,994,000
Charges for general and administrative services		36,078,000	24,059,000
Depreciation and amortization		6,940,000	6,033,000
Other (income)/expense, net		(5,073,000)	(2,668,000)
Interest expense		60,930,000	60,305,000
Total expenses		532,938,000	414,171,000
Employee labor and benefit costs capitalized		49,300,000	46,100,000
Short-term note payable to ONEOK [Member] | ONEOK, Inc. [Member]
Operations and maintenance [Abstract]
Weighted-average interest rate		0.92%	0.96%
Note Payable, Interest Rate Description		Principal under this note payable bears interest based on ONEOK’s weighted-average cost of short-term debt, plus a utilization fee of 50 basis points, calculated monthly.
Long-term line of credit with ONEOK [Member] | ONEOK, Inc. [Member]
Operations and maintenance [Abstract]
Weighted-average interest rate		5.79%	6.43%
Long-term line of credit with ONEOK	$ 1,100,000,000
Line of Credit Facility, Interest Rate Description		The interest rate on the revolver was reset each year based on ONEOK’s outstanding debt plus an adjustment of 50 basis points for ONEOK’s cost to administer the program.