SUPPLEMENTAL CONDENSED CONSOLIDATING FINANCIAL INFORMATION (Tables)

12 Months Ended

Dec. 31, 2017

Condensed Financial Information of Parent Company Only Disclosure [Abstract]

Condensed Consolidating Statements of Income

	Year Ended December 31, 2017
	Parent Issuer & Guarantor			Subsidiary Issuer & Guarantor			Guarantor Subsidiary			Combined Non-Guarantor Subsidiaries			Consolidating Entries			Total
	(Millions of dollars)
Revenues
Commodity sales	$	—		$	—		$	—		$	9,862.7		$	—		$	9,862.7
Services	—			—			—			2,313.2			(2.0		)	2,311.2
Total revenues	—			—			—			12,175.9			(2.0		)	12,173.9
Cost of sales and fuel (exclusive of items shown separately below)	—			—			—			9,538.0			—			9,538.0
Operating expenses	28.7			—			9.2			1,204.0			(2.0		)	1,239.9
Impairment of long-lived assets	—			—			—			16.0			—			16.0
Gain on sale of assets	—			—			—			(0.9		)	—			(0.9		)
Operating income	(28.7		)	—			(9.2		)	1,418.8			—			1,380.9
Equity in net earnings from investments	1,236.6			1,215.7			1,224.9			100.7			(3,618.6		)	159.3
Impairment of equity investments	—			—			—			(4.3		)	—			(4.3		)
Other income (expense), net	(1.4		)	353.1			353.1			(8.0		)	(706.2		)	(9.4		)
Interest expense, net	(137.1		)	(353.1		)	(353.1		)	(348.6		)	706.2			(485.7		)
Income before income taxes	1,069.4			1,215.7			1,215.7			1,158.6			(3,618.6		)	1,040.8
Income taxes	(480.2		)	—			—			32.9			—			(447.3		)
Net income	589.2			1,215.7			1,215.7			1,191.5			(3,618.6		)	593.5
Less: Net income attributable to noncontrolling interests	201.4			—			—			4.3			—			205.7
Net income attributable to ONEOK	387.8			1,215.7			1,215.7			1,187.2			(3,618.6		)	387.8
Less: Preferred stock dividends	0.8			—			—			—			—			0.8
Net income available to common shareholders	$	387.0		$	1,215.7		$	1,215.7		$	1,187.2		$	(3,618.6	)	$	387.0

	Year Ending December 31, 2016
	Parent Issuer & Guarantor			Subsidiary Issuer & Guarantor			Guarantor Subsidiary			Combined Non-Guarantor Subsidiaries			Consolidating Entries			Total
	(Millions of dollars)
Revenues
Commodity sales	$	—		$	—		$	—		$	6,858.5		$	—		$	6,858.5
Services	—			—			—			2,064.3			(1.8		)	2,062.5
Total revenues	—			—			—			8,922.8			(1.8		)	8,921.0
Cost of sales and fuel (exclusive of items shown separately below)	—			—			—			6,496.1			—			6,496.1
Operating expenses	28.8			—			—			1,121.8			(1.8		)	1,148.8
(Gain) loss on sale of assets	0.3			—			—			(9.9		)	—			(9.6		)
Operating income	(29.1		)	—			—			1,314.8			—			1,285.7
Equity in net earnings from investments	1,063.9			1,066.8			1,066.8			69.7			(3,127.5		)	139.7
Other income (expense), net	5.1			373.5			373.5			(2.8		)	(747.0		)	2.3
Interest expense, net	(102.9		)	(373.5		)	(373.5		)	(366.8		)	747.0			(469.7		)
Income before income taxes	937.0			1,066.8			1,066.8			1,014.9			(3,127.5		)	958.0
Income taxes	(199.0		)	—			—			(13.4		)	—			(212.4		)
Income from continuing operations	738.0			1,066.8			1,066.8			1,001.5			(3,127.5		)	745.6
Income (loss) from discontinued operations, net of tax	—			—			—			(2.1		)	—			(2.1		)
Net income	738.0			1,066.8			1,066.8			999.4			(3,127.5		)	743.5
Less: Net income attributable to noncontrolling interests	386.0			—			—			5.5			—			391.5
Net income attributable to ONEOK	$	352.0		$	1,066.8		$	1,066.8		$	993.9		$	(3,127.5	)	$	352.0

	Year Ending December 31, 2015
	Parent Issuer & Guarantor			Subsidiary Issuer & Guarantor			Guarantor Subsidiary			Combined Non-Guarantor Subsidiaries			Consolidating Entries			Total
	(Millions of dollars)
Revenues
Commodity sales	$	—		$	—		$	—		$	6,098.3		$	—		$	6,098.3
Services	—			—			—			1,669.8			(4.9		)	1,664.9
Total revenues	—			—			—			7,768.1			(4.9		)	7,763.2
Cost of sales and fuel (exclusive of items shown separately below)	—			—			—			5,641.1			—			5,641.1
Operating expenses	1.2			—			—			1,051.5			(4.9		)	1,047.8
Impairment of long-lived assets	—			—			—			83.7			—			83.7
Gain on sale of assets	—			—			—			(5.6		)	—			(5.6		)
Operating income	(1.2		)	—			—			997.4			—			996.2
Equity in net earnings from investments	583.8			589.5			589.5			58.4			(1,695.9		)	125.3
Impairment of equity investments	—			—			—			(180.6		)	—			(180.6		)
Other income (expense), net	4.0			371.0			371.0			(6.2		)	(742.0		)	(2.2		)
Interest expense, net	(85.1		)	(371.0		)	(371.0		)	(331.7		)	742.0			(416.8		)
Income before income taxes	501.5			589.5			589.5			537.3			(1,695.9		)	521.9
Income taxes	(130.7		)	—			—			(5.9		)	—			(136.6		)
Income from continuing operations	370.8			589.5			589.5			531.4			(1,695.9		)	385.3
Income (loss) from discontinued operations, net of tax	—			—			—			(6.1		)	—			(6.1		)
Net income	370.8			589.5			589.5			525.3			(1,695.9		)	379.2
Less: Net income attributable to noncontrolling interests	125.8			—			—			8.4			—			134.2
Net income attributable to ONEOK	$	245.0		$	589.5		$	589.5		$	516.9		$	(1,695.9	)	$	245.0

Condensed Consolidating Statements of Comprehensive Income

	Year Ended December 31, 2017
	Parent Issuer & Guarantor			Subsidiary Issuer & Guarantor			Guarantor Subsidiary			Combined Non-Guarantor Subsidiaries			Consolidating Entries			Total
	(Millions of dollars)
Net income	$	589.2		$	1,215.7		$	1,215.7		$	1,191.5		$	(3,618.6	)	$	593.5
Other comprehensive income (loss), net of tax
Unrealized gains (losses) on derivatives, net of tax	19.1			(72.2		)	(40.6		)	(8.8		)	81.1			(21.4		)
Realized (gains) losses on derivatives in net income, net of tax	2.5			86.5			69.6			44.3			(139.2		)	63.7
Change in pension and postretirement benefit plan liability, net of tax	(4.2		)	—			—			—			—			(4.2		)
Other comprehensive income (loss) on investments in unconsolidated affiliates, net of tax	—			(1.1		)	(1.1		)	(1.0		)	2.2			(1.0		)
Total other comprehensive income (loss), net of tax	17.4			13.2			27.9			34.5			(55.9		)	37.1
Comprehensive income	606.6			1,228.9			1,243.6			1,226.0			(3,674.5		)	630.6
Less: Comprehensive income attributable to noncontrolling interests	232.4			—			—			4.3			—			236.7
Comprehensive income attributable to ONEOK	$	374.2		$	1,228.9		$	1,243.6		$	1,221.7		$	(3,674.5	)	$	393.9

	Year Ending December 31, 2016
	Parent Issuer & Guarantor			Subsidiary Issuer & Guarantor			Guarantor Subsidiary			Combined Non-Guarantor Subsidiaries			Consolidating Entries			Total
	(Millions of dollars)
Net income	$	738.0		$	1,066.8		$	1,066.8		$	999.4		$	(3,127.5	)	$	743.5
Other comprehensive income (loss), net of tax
Unrealized gains (losses) on derivatives, net of tax	—			(35.8		)	(78.5		)	(108.8		)	192.8			(30.3		)
Realized (gains) losses on derivatives in net income, net of tax	2.1			(10.7		)	(26.4		)	(33.4		)	61.4			(7.0		)
Change in pension and postretirement benefit plan liability, net of tax	(16.7		)	—			—			—			—			(16.7		)
Other comprehensive income (loss) on investments in unconsolidated affiliates, net of tax	—			(1.8		)	(1.8		)	(3.3		)	5.4			(1.5		)
Total other comprehensive income (loss), net of tax	(14.6		)	(48.3		)	(106.7		)	(145.5		)	259.6			(55.5		)
Comprehensive income	723.4			1,018.5			960.1			853.9			(2,867.9		)	688.0
Less: Comprehensive income attributable to noncontrolling interests	357.6			—			—			5.5			—			363.1
Comprehensive income attributable to ONEOK	$	365.8		$	1,018.5		$	960.1		$	848.4		$	(2,867.9	)	$	324.9

	Year Ending December 31, 2015
	Parent Issuer & Guarantor		Subsidiary Issuer & Guarantor			Guarantor Subsidiary			Combined Non-Guarantor Subsidiaries			Consolidating Entries			Total
	(Millions of dollars)
Net income	$	370.8	$	589.5		$	589.5		$	525.3		$	(1,695.9	)	$	379.2
Other comprehensive income (loss), net of tax
Unrealized gains (losses) on derivatives, net of tax	—		47.5			70.1			111.5			(187.7		)	41.4
Realized (gains) losses on derivatives in net income, net of tax	2.1		(67.0		)	(81.1		)	(137.9		)	229.2			(54.7		)
Unrealized holding gains (losses) on available-for-sale securities, net of tax	—		—			—			(1.0		)	—			(1.0		)
Change in pension and postretirement benefit plan liability, net of tax	15.4		—			—			—			—			15.4
Other comprehensive income (loss) on investments in unconsolidated affiliates, net of tax	—		(1.9		)	(1.9		)	(3.5		)	5.7			(1.6		)
Total other comprehensive income (loss), net of tax	17.5		(21.4		)	(12.9		)	(30.9		)	47.2			(0.5		)
Comprehensive income	388.3		568.1			576.6			494.4			(1,648.7		)	378.7
Less: Comprehensive income attributable to noncontrolling interests	116.2		—			—			8.4			—			124.6
Comprehensive income attributable to ONEOK	$	272.1	$	568.1		$	576.6		$	486.0		$	(1,648.7	)	$	254.1

Condensed Consolidating Balance Sheets

	December 31, 2017
	Parent Issuer & Guarantor		Subsidiary Issuer & Guarantor		Guarantor Subsidiary		Combined Non-Guarantor Subsidiaries		Consolidating Entries			Total
Assets	(Millions of dollars)
Current assets
Cash and cash equivalents	$	37.2	$	—	$	—	$	—	$	—		$	37.2
Accounts receivable, net	—		—		—		1,203.0		—			1,203.0
Materials and supplies	—		—		—		90.3		—			90.3
Natural gas and natural gas liquids in storage	—		—		—		342.3		—			342.3
Other current assets	9.8		1.3		—		80.6		—			91.7
Total current assets	47.0		1.3		—		1,716.2		—			1,764.5
Property, plant and equipment
Property, plant and equipment	128.3		—		—		15,431.3		—			15,559.6
Accumulated depreciation and amortization	86.4		—		—		2,775.1		—			2,861.5
Net property, plant and equipment	41.9		—		—		12,656.2		—			12,698.1
Investments and other assets
Investments	5,752.1		3,133.7		8,058.4		803.0		(16,744.0		)	1,003.2
Intercompany notes receivable	2,926.9		8,627.8		3,703.1		—		(15,257.8		)	—
Other assets	416.9		0.2		—		1,007.4		(44.4		)	1,380.1
Total investments and other assets	9,095.9		11,761.7		11,761.5		1,810.4		(32,046.2		)	2,383.3
Total assets	$	9,184.8	$	11,763.0	$	11,761.5	$	16,182.8	$	(32,046.2	)	$	16,845.9
Liabilities and equity
Current liabilities
Current maturities of long-term debt	$	—	$	425.0	$	—	$	7.7	$	—		$	432.7
Short-term borrowings	614.7		—		—		—		—			614.7
Accounts payable	12.0		—		—		1,128.6		—			1,140.6
Other current liabilities	65.9		85.0		—		328.4		—			479.3
Total current liabilities	692.6		510.0		—		1,464.7		—			2,667.3
Intercompany debt	—		—		8,627.8		6,630.0		(15,257.8		)	—
Long-term debt, excluding current maturities	2,726.4		5,336.4		—		28.8		—			8,091.6
Deferred credits and other liabilities	237.9		—		—		208.1		(44.4		)	401.6
Commitments and contingencies
Equity
Equity excluding noncontrolling interests in consolidated subsidiaries	5,527.9		5,916.6		3,133.7		7,693.7		(16,744.0		)	5,527.9
Noncontrolling interests in consolidated subsidiaries	—		—		—		157.5		—			157.5
Total equity	5,527.9		5,916.6		3,133.7		7,851.2		(16,744.0		)	5,685.4
Total liabilities and equity	$	9,184.8	$	11,763.0	$	11,761.5	$	16,182.8	$	(32,046.2	)	$	16,845.9

	December 31, 2016
	Parent Issuer & Guarantor		Subsidiary Issuer & Guarantor		Guarantor Subsidiary		Combined Non-Guarantor Subsidiaries		Consolidating Entries			Total
Assets	(Millions of dollars)
Current assets
Cash and cash equivalents	$	248.5	$	—	$	0.4	$	—	$	—		$	248.9
Accounts receivable, net	—		—		—		872.4		—			872.4
Materials and supplies	—		—		—		60.9		—			60.9
Natural gas and natural gas liquids in storage	—		—		—		140.0		—			140.0
Other current assets	7.2		—		—		99.7		—			106.9
Assets of discontinued operations	—		—		—		0.6		—			0.6
Total current assets	255.7		—		0.4		1,173.6		—			1,429.7
Property, plant and equipment
Property, plant and equipment	139.8		—		—		14,938.7		—			15,078.5
Accumulated depreciation and amortization	90.4		—		—		2,416.7		—			2,507.1
Net property, plant and equipment	49.4		—		—		12,522.0		—			12,571.4
Investments and other assets
Investments	2,931.9		3,222.1		6,805.4		631.1		(12,631.7		)	958.8
Intercompany notes receivable	205.2		10,615.0		7,031.3		—		(17,851.5		)	—
Goodwill and intangible assets	—		—		—		1,005.4		—			1,005.4
Other assets	103.4		47.5		—		12.1		—			163.0
Assets of discontinued operations	—		—		—		10.5		—			10.5
Total investments and other assets	3,240.5		13,884.6		13,836.7		1,659.1		(30,483.2		)	2,137.7
Total assets	$	3,545.6	$	13,884.6	$	13,837.1	$	15,354.7	$	(30,483.2	)	$	16,138.8
Liabilities and equity
Current liabilities
Current maturities of long-term debt	$	3.0	$	400.0	$	—	$	7.7	$	—		$	410.7
Short-term borrowings	—		1,110.3		—		—		—			1,110.3
Accounts payable	13.0		—		—		861.7		—			874.7
Commodity imbalances	—		—		—		142.6		—			142.6
Accrued interest	25.4		87.1		—		—		—			112.5
Other current liabilities	19.3		12.8		—		134.1		—			166.2
Liabilities of discontinued operations	—		—		—		19.8		—			19.8
Total current liabilities	60.7		1,610.2		—		1,165.9		—			2,836.8
Intercompany debt	—		—		10,615.0		7,236.5		(17,851.5		)	—
Long-term debt, excluding current maturities	1,628.7		6,254.7		—		36.6		—			7,920.0
Deferred credits and other liabilities	1,667.5		—		—		285.6		—			1,953.1
Commitments and contingencies
Equity
Equity excluding noncontrolling interests in consolidated subsidiaries	188.7		6,019.7		3,222.1		6,472.0		(15,713.8		)	188.7
Noncontrolling interests in consolidated subsidiaries	—		—		—		158.1		3,082.1			3,240.2
Total equity	188.7		6,019.7		3,222.1		6,630.1		(12,631.7		)	3,428.9
Total liabilities and equity	$	3,545.6	$	13,884.6	$	13,837.1	$	15,354.7	$	(30,483.2	)	$	16,138.8

Condensed Consolidating Statements of Cash Flows

	Year Ended December 31, 2017
	Parent Issuer & Guarantor			Subsidiary Issuer & Guarantor			Guarantor Subsidiary			Combined Non-Guarantor Subsidiaries			Consolidating Entries			Total
	(Millions of dollars)
Operating activities
Cash provided by operating activities	$	947.4		$	1,348.3		$	59.0		$	1,353.7		$	(2,393.0	)	$	1,315.4
Investing activities
Capital expenditures	—			—			—			(512.4		)	—			(512.4		)
Contributions to unconsolidated affiliates	—			—			(83.0		)	(4.9		)	—			(87.9		)
Other investing activities	—			—			14.8			17.9			—			32.7
Cash used in investing activities	—			—			(68.2		)	(499.4		)	—			(567.6		)
Financing activities
Dividends paid	(829.4		)	(1,332.0		)	(1,332.0		)	—			2,664.0			(829.4		)
Distributions to noncontrolling interests	—			—			—			(5.3		)	(271.0		)	(276.3		)
Intercompany borrowings (advances), net	(2,500.7		)	2,001.2			1,340.8			(841.3		)	—			—
Borrowing (repayment) of short-term borrowings, net	614.7			(1,110.3		)	—			—			—			(495.6		)
Issuance of long-term debt, net of discounts	1,190.5			—			—			—			—			1,190.5
Repayment of long-term debt	(87.1		)	(900.0		)	—			(7.7		)	—			(994.8		)
Issuance of common stock	471.4			—			—			—			—			471.4
Other	(18.1		)	(7.2		)	—			—			—			(25.3		)
Cash provided by (used in) financing activities	(1,158.7		)	(1,348.3		)	8.8			(854.3		)	2,393.0			(959.5		)
Change in cash and cash equivalents	(211.3		)	—			(0.4		)	—			—			(211.7		)
Cash and cash equivalents at beginning of period	248.5			—			0.4			—			—			248.9
Cash and cash equivalents at end of period	$	37.2		$	—		$	—		$	—		$	—		$	37.2

	Year Ending December 31, 2016
	Parent Issuer & Guarantor			Subsidiary Issuer & Guarantor			Guarantor Subsidiary			Combined Non-Guarantor Subsidiaries			Consolidating Entries			Total
	(Millions of dollars)
Operating activities
Cash provided by operating activities	$	717.0		$	1,334.5		$	70.0		$	1,353.9		$	(2,122.1	)	$	1,353.3
Investing activities
Capital expenditures	(0.2		)	—			—			(624.4		)	—			(624.6		)
Other investing activities	—			—			34.9			(25.7		)	—			9.2
Cash provided by (used in) investing activities	(0.2		)	—			34.9			(650.1		)	—			(615.4		)
Financing activities
Dividends paid	(517.6		)	(1,332.0		)	(1,332.0		)	—			2,664.0			(517.6		)
Distributions to noncontrolling interests	—			—			—			(7.5		)	(541.9		)	(549.4		)
Intercompany borrowings (advances), net	(63.1		)	(470.8		)	1,222.4			(688.5		)	—			—
Borrowing (repayment) of short-term borrowings, net	—			563.9			—			—			—			563.9
Issuance of long-term debt, net of discounts	—			1,000.0			—			—			—			1,000.0
Debt financing costs	—			(2.8		)	—			—			—			(2.8		)
Repayment of long-term debt	(0.3		)	(1,100.0		)	—			(7.7		)	—			(1,108.0		)
Issuance of common stock	22.0			—			—			—			—			22.0
Other	(1.7		)	7.2			—			(0.1		)	—			5.4
Cash used in financing activities	(560.7		)	(1,334.5		)	(109.6		)	(703.8		)	2,122.1			(586.5		)
Change in cash and cash equivalents	156.1			—			(4.7		)	—			—			151.4
Change in cash and cash equivalents included in discontinued operations	(0.1		)	—			—			—			—			(0.1		)
Change in cash and cash equivalents included in continuing operations	156.0			—			(4.7		)	—			—			151.3
Cash and cash equivalents at beginning of period	92.5			—			5.1			—			—			97.6
Cash and cash equivalents at end of period	$	248.5		$	—		$	0.4		$	—		$	—		$	248.9

	Year Ending December 31, 2015
	Parent Issuer & Guarantor			Subsidiary Issuer & Guarantor			Guarantor Subsidiary			Combined Non-Guarantor Subsidiaries			Consolidating Entries			Total
	(Millions of dollars)
Operating activities
Cash provided by operating activities	$	650.3		$	1,196.7		$	66.9		$	1,045.7		$	(1,936.8	)	$	1,022.8
Investing activities
Capital expenditures	(0.1		)	—			—			(1,188.2		)	—			(1,188.3		)
Contributions to investments	(671.0		)	—			—			(27.5		)	671.0			(27.5		)
Other investing activities	—			—			24.1			1.0			—			25.1
Cash provided by (used in) investing activities	(671.1		)	—			24.1			(1,214.7		)	671.0			(1,190.7		)
Financing activities
Dividends paid	(509.2		)	(1,230.5		)	(1,230.5		)	—			2,461.0			(509.2		)
Distributions to noncontrolling interests	—			—			—			(11.7		)	(524.2		)	(535.9		)
Intercompany borrowings (advances), net	4.6			(1,295.1		)	1,102.1			188.4			—			—
Borrowing (repayment) of short-term borrowings, net	—			(509.0		)	—			—			—			(509.0		)
Issuance of long-term debt, net of discounts	492.6			798.9			—			—			—			1,291.5
Debt financing costs	(9.8		)	(7.7		)	—			—			—			(17.5		)
Repayment of long-term debt	(0.1		)	—			—			(7.7		)	—			(7.8		)
Issuance of common stock	20.7			—			—			—			—			20.7
Issuance of common units, net of issuance costs	—			1,025.7			—			—			(650.0		)	375.7
Contribution from general partner	—			21.0			—			—			(21.0		)	—
Other	(15.8		)	—			—			—			—			(15.8		)
Cash provided by (used) in financing activities	(17.0		)	(1,196.7		)	(128.4		)	169.0			1,265.8			92.7
Change in cash and cash equivalents	(37.8		)	—			(37.4		)	—			—			(75.2		)
Cash and cash equivalents at beginning of period	130.3			—			42.5			—			—			172.8
Cash and cash equivalents at end of period	$	92.5		$	—		$	5.1		$	—		$	—		$	97.6