Guarantee of Securities of Subsidiaries (Tables)

9 Months Ended

Sep. 30, 2016

Condensed Financial Information of Parent Company Only Disclosure [Abstract]

Condensed Consolidating Balance Sheet

Condensed Consolidating Balance Sheets as of September 30, 2016

(Millions)

Assets	Parent Guarantor		Subsidiary Issuer		Non-guarantor Subsidiaries		Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Cash and cash equivalents	$	0.3	$	107.3	$	3.8	$	—		$	111.4
Receivables	—		—		119.5		—			119.5
Receivables - affiliate	—		—		7.0		(7.0		)	—
Gas and liquids stored underground	—		—		12.4		—			12.4
Prepayments	0.4		—		19.7		—			20.1
Advances to affiliates	—		—		127.7		(127.7		)	—
Other current assets	—		—		20.7		(11.8		)	8.9
Total current assets	0.7		107.3		310.8		(146.5		)	272.3
Investment in consolidated subsidiaries	2,344.6		6,608.7		—		(8,953.3		)	—
Property, plant and equipment, gross	0.6		—		10,155.6		—			10,156.2
Less–accumulated depreciation    and amortization	0.6		—		2,257.4		—			2,258.0
Property, plant and equipment, net	—		—		7,898.2		—			7,898.2
Other noncurrent assets	—		3.4		471.5		(2.7		)	472.2
Advances to affiliates – noncurrent	2,140.5		504.1		61.9		(2,706.5		)	—
Total other assets	2,140.5		507.5		533.4		(2,709.2		)	472.2
Total Assets	$	4,485.8	$	7,223.5	$	8,742.4	$	(11,809.0	)	$	8,642.7

Liabilities and Partners' Capital	Parent Guarantor		Subsidiary Issuer		Non-guarantor Subsidiaries		Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Payables	$	0.3	$	0.1	$	117.8	$	—		$	118.2
Payable to affiliates	1.4		—		7.0		(7.0		)	1.4
Advances from affiliates	—		127.7		—		(127.7		)	—
Other current liabilities	—		35.0		191.2		(14.5		)	211.7
Total current liabilities	1.7		162.8		316.0		(149.2		)	331.3
Long-term debt and capital lease     obligation	—		2,513.6		1,113.2		—			3,626.8
Payable to affiliate - noncurrent	16.0		—		—		—			16.0
Advances from affiliates - noncurrent	—		2,202.4		504.1		(2,706.5		)	—
Other noncurrent liabilities	—		0.1		200.4		—			200.5
Total other liabilities and deferred     credits	16.0		2,202.5		704.5		(2,706.5		)	216.5
Total partners' capital	4,468.1		2,344.6		6,608.7		(8,953.3		)	4,468.1
Total Liabilities and Partners'     Capital	$	4,485.8	$	7,223.5	$	8,742.4	$	(11,809.0	)	$	8,642.7

Condensed Consolidating Balance Sheets as of December 31, 2015

(Millions)

Assets	Parent  Guarantor		Subsidiary Issuer		Non-guarantor Subsidiaries		Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Cash and cash equivalents	$	—	$	0.3	$	2.8	$	—		$	3.1
Receivables	—		—		129.5		—			129.5
Receivables - affiliate	—		—		7.0		(7.0		)	—
Gas and liquids stored underground	—		—		10.7		—			10.7
Prepayments	0.2		—		16.7		—			16.9
Advances to affiliates	—		21.0		107.7		(128.7		)	—
Other current assets	—		—		12.8		(3.2		)	9.6
Total current assets	0.2		21.3		287.2		(138.9		)	169.8
Investment in consolidated subsidiaries	2,153.5		7,067.6		—		(9,221.1		)	—
Property, plant and equipment, gross	0.6		—		9,706.0		—			9,706.6
Less–accumulated depreciation    and amortization	0.6		—		2,051.6		—			2,052.2
Property, plant and equipment, net	—		—		7,654.4		—			7,654.4
Other noncurrent assets	0.4		3.0		472.7		—			476.1
Advances to affiliates – noncurrent	2,190.2		466.3		1,113.4		(3,769.9		)	—
Total other assets	2,190.6		469.3		1,586.1		(3,769.9		)	476.1
Total Assets	$	4,344.3	$	7,558.2	$	9,527.7	$	(13,129.9	)	$	8,300.3

Liabilities and Partners' Capital	Parent Guarantor		Subsidiary Issuer		Non-guarantor Subsidiaries		Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Payables	$	0.3	$	0.1	$	118.2	$	—		$	118.6
Payable to affiliates	1.3		—		7.0		(7.0		)	1.3
Advances from affiliates	—		107.7		21.0		(128.7		)	—
Other current liabilities	—		20.9		176.8		(3.2		)	194.5
Total current liabilities	1.6		128.7		323.0		(138.9		)	314.4
Long-term debt and capital lease     obligation	—		1,972.4		1,486.9		—			3,459.3
Payable to affiliate - noncurrent	16.0		—		—		—			16.0
Advances from affiliates - noncurrent	—		3,303.6		466.3		(3,769.9		)	—
Other noncurrent liabilities	—		—		183.9		—			183.9
Total other liabilities and deferred     credits	16.0		3,303.6		650.2		(3,769.9		)	199.9
Total partners' capital	4,326.7		2,153.5		7,067.6		(9,221.1		)	4,326.7
Total Liabilities and Partners'     Capital	$	4,344.3	$	7,558.2	$	9,527.7	$	(13,129.9	)	$	8,300.3

Condensed Consolidating Statements of Income

Condensed Consolidating Statements of Income for the Three Months Ended September 30, 2016

(Millions)

	Parent Guarantor			Subsidiary Issuer			Non-guarantor Subsidiaries			Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Operating Revenues:
Transportation	$	—		$	—		$	281.9		$	(22.3	)	$	259.6
Parking and lending	—			—			5.1			(0.2		)	4.9
Storage	—			—			23.4			—			23.4
Other	—			—			15.4			—			15.4
Total operating revenues	—			—			325.8			(22.5		)	303.3
Operating Costs and Expenses:
Fuel and transportation	—			—			41.6			(22.5		)	19.1
Operation and maintenance	—			—			52.1			—			52.1
Administrative and general	—			—			34.4			—			34.4
Other operating costs and expenses	0.1			—			103.9			—			104.0
Total operating costs and expenses	0.1			—			232.0			(22.5		)	209.6
Operating (loss) income	(0.1		)	—			93.8			—			93.7
Other Deductions (Income):
Interest expense	—			34.6			13.8			—			48.4
Interest (income) expense - affiliates, net	(9.7		)	11.7			(2.0		)	—			—
Interest income	—			—			(0.1		)	—			(0.1		)
Equity in earnings of subsidiaries	(37.7		)	(84.0		)	—			121.7			—
Miscellaneous other income, net	—			—			(1.9		)	—			(1.9		)
Total other (income) deductions	(47.4		)	(37.7		)	9.8			121.7			46.4
Income (loss) before income taxes	47.3			37.7			84.0			(121.7		)	47.3
Income taxes	—			—			—			—			—
Net income (loss)	$	47.3		$	37.7		$	84.0		$	(121.7	)	$	47.3

Condensed Consolidating Statements of Income for the Three Months Ended September 30, 2015

(Millions)

	Parent Guarantor			Subsidiary Issuer			Non-guarantor Subsidiaries			Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Operating Revenues:
Transportation	$	—		$	—		$	277.1		$	(21.5	)	$	255.6
Parking and lending	—			—			2.3			—			2.3
Storage	—			—			20.4			—			20.4
Other	—			—			15.8			—			15.8
Total operating revenues	—			—			315.6			(21.5		)	294.1
Operating Costs and Expenses:
Fuel and transportation	—			—			46.6			(21.5		)	25.1
Operation and maintenance	—			—			54.0			—			54.0
Administrative and general	0.2			—			31.5			—			31.7
Other operating costs and expenses	—			—			102.6			—			102.6
Total operating costs and expenses	0.2			—			234.7			(21.5		)	213.4
Operating (loss) income	(0.2		)	—			80.9			—			80.7
Other Deductions (Income):
Interest expense	—			26.1			17.0			—			43.1
Interest (income) expense - affiliates, net	(7.3		)	9.7			(2.4		)	—			—
Interest income	—			—			(0.1		)	—			(0.1		)
Equity in earnings of subsidiaries	(31.2		)	(67.0		)	—			98.2			—
Miscellaneous other income, net	—			—			(0.7		)	—			(0.7		)
Total other (income) deductions	(38.5		)	(31.2		)	13.8			98.2			42.3
Income (loss) before income taxes	38.3			31.2			67.1			(98.2		)	38.4
Income taxes	—			—			0.1			—			0.1
Net income (loss)	$	38.3		$	31.2		$	67.0		$	(98.2	)	$	38.3

Condensed Consolidating Statements of Income for the Nine Months Ended September 30, 2016

(Millions)

	Parent Guarantor			Subsidiary Issuer			Non-guarantor Subsidiaries			Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Operating Revenues:
Transportation	$	—		$	—		$	901.0		$	(65.7	)	$	835.3
Parking and lending	—			—			14.6			(1.2		)	13.4
Storage	—			—			68.0			—			68.0
Other	—			—			37.9			—			37.9
Total operating revenues	—			—			1,021.5			(66.9		)	954.6
Operating Costs and Expenses:
Fuel and transportation	—			—			117.9			(66.9		)	51.0
Operation and maintenance	—			—			143.8			—			143.8
Administrative and general	0.1			—			104.5			—			104.6
Other operating costs and expenses	0.3			—			310.3			—			310.6
Total operating costs and expenses	0.4			—			676.5			(66.9		)	610.0
Operating (loss) income	(0.4		)	—			345.0			—			344.6
Other Deductions (Income):
Interest expense	—			91.1			45.3			—			136.4
Interest (income) expense - affiliates, net	(27.6		)	35.2			(7.6		)	—			—
Interest income	—			—			(0.3		)	—			(0.3		)
Equity in earnings of subsidiaries	(187.0		)	(313.3		)	—			500.3			—
Miscellaneous other income, net	0.2			—			(6.1		)	—			(5.9		)
Total other (income) deductions	(214.4		)	(187.0		)	31.3			500.3			130.2
Income (loss) before income taxes	214.0			187.0			313.7			(500.3		)	214.4
Income taxes	—			—			0.4			—			0.4
Net income (loss)	$	214.0		$	187.0		$	313.3		$	(500.3	)	$	214.0

Condensed Consolidating Statements of Income for the Nine Months Ended September 30, 2015

(Millions)

	Parent Guarantor			Subsidiary Issuer			Non-guarantor Subsidiaries			Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Operating Revenues:
Transportation	$	—		$	—		$	867.3		$	(65.2	)	$	802.1
Parking and lending	—			—			8.1			(0.2		)	7.9
Storage	—			—			60.6			—			60.6
Other	—			—			51.8			—			51.8
Total operating revenues	—			—			987.8			(65.4		)	922.4
Operating Costs and Expenses:
Fuel and transportation	—			—			143.4			(65.4		)	78.0
Operation and maintenance	—			—			148.7			—			148.7
Administrative and general	—			—			94.1			—			94.1
Other operating costs and expenses	0.2			—			312.0			—			312.2
Total operating costs and expenses	0.2			—			698.2			(65.4		)	633.0
Operating (loss) income	(0.2		)	—			289.6			—			289.4
Other Deductions (Income):
Interest expense	—			77.9			56.3			—			134.2
Interest (income) expense - affiliates, net	(21.2		)	28.3			(7.1		)	—			—
Interest income	—			—			(0.3		)	—			(0.3		)
Equity in earnings of subsidiaries	(135.4		)	(241.6		)	—			377.0			—
Miscellaneous other income, net	—			—			(1.3		)	—			(1.3		)
Total other (income) deductions	(156.6		)	(135.4		)	47.6			377.0			132.6
Income (loss) before income taxes	156.4			135.4			242.0			(377.0		)	156.8
Income taxes	—			—			0.4			—			0.4
Net income (loss)	$	156.4		$	135.4		$	241.6		$	(377.0	)	$	156.4

Condensed Consolidating Statements Of Comprehensive Income

Condensed Consolidating Statements of Comprehensive Income for the Three Months Ended September 30, 2016

(Millions)

	Parent Guarantor		Subsidiary Issuer		Non-guarantor Subsidiaries		Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Net income (loss)	$	47.3	$	37.7	$	84.0	$	(121.7	)	$	47.3
Other comprehensive income (loss):
Reclassification adjustment transferred     to Net income from cash flow hedges	0.6		0.6		0.2		(0.8		)	0.6
Pension and other postretirement     benefit costs	0.6		0.6		0.6		(1.2		)	0.6
Total Comprehensive Income (Loss)	$	48.5	$	38.9	$	84.8	$	(123.7	)	$	48.5

Condensed Consolidating Statements of Comprehensive Income for the Three Months Ended September 30, 2015

(Millions)

	Parent Guarantor		Subsidiary Issuer		Non-guarantor Subsidiaries		Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Net income (loss)	$	38.3	$	31.2	$	67.0	$	(98.2	)	$	38.3
Other comprehensive income (loss):
Reclassification adjustment transferred     to Net income from cash flow hedges	0.6		0.6		0.2		(0.8		)	0.6
Total Comprehensive Income (Loss)	$	38.9	$	31.8	$	67.2	$	(99.0	)	$	38.9

Condensed Consolidating Statements of Comprehensive Income for the Nine Months Ended September 30, 2016

(Millions)

	Parent Guarantor		Subsidiary Issuer		Non-guarantor Subsidiaries		Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Net income (loss)	$	214.0	$	187.0	$	313.3	$	(500.3	)	$	214.0
Other comprehensive income (loss):
Reclassification adjustment transferred     to Net income from cash flow hedges	1.8		1.8		0.6		(2.4		)	1.8
Pension and other postretirement     benefit costs	2.3		2.3		2.3		(4.6		)	2.3
Total Comprehensive Income (Loss)	$	218.1	$	191.1	$	316.2	$	(507.3	)	$	218.1

Condensed Consolidating Statements of Comprehensive Income for the Nine Months Ended September 30, 2015

(Millions)

	Parent Guarantor			Subsidiary Issuer			Non-guarantor Subsidiaries			Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Net income (loss)	$	156.4		$	135.4		$	241.6		$	(377.0	)	$	156.4
Other comprehensive income (loss):
Reclassification adjustment transferred     to Net income from cash flow hedges	1.8			1.8			0.6			(2.4		)	1.8
Pension and other postretirement     benefit costs	(4.3		)	(4.3		)	(4.3		)	8.6			(4.3		)
Total Comprehensive Income (Loss)	$	153.9		$	132.9		$	237.9		$	(370.8	)	$	153.9

Condensed Consolidating Statements of Cash Flows

Condensed Consolidating Statements of Cash Flow for the Nine Months Ended September 30, 2016

(Millions)

	Parent Guarantor			Subsidiary  Issuer			Non-guarantor Subsidiaries			Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Net cash provided by (used in)     operating activities	$	27.3		$	(108.3	)	$	535.2		$	—		$	454.2
INVESTING ACTIVITIES:
Capital expenditures	—			—			(432.4		)	—			(432.4		)
Proceeds from sale of operating assets	—			—			0.2			—			0.2
Advances to affiliates, net	49.7			(16.8		)	256.5			(289.4		)	—
Net cash provided by (used in)     investing activities	49.7			(16.8		)	(175.7		)	(289.4		)	(432.2		)
FINANCING ACTIVITIES:
Proceeds from long-term debt, net of     issuance cost	—			539.1			—			—			539.1
Proceeds from borrowings on revolving     credit agreement	—			—			255.0			—			255.0
Repayment of borrowings on revolving     credit agreement, including financing fees	—			(0.8		)	(630.0		)	—			(630.8		)
Principal payment of capital lease     obligation	—			—			(0.3		)	—			(0.3		)
Advances from affiliates, net	—			(306.2		)	16.8			289.4			—
Distributions paid	(76.7		)	—			—			—			(76.7		)
Net cash (used in) provided by     financing activities	(76.7		)	232.1			(358.5		)	289.4			86.3
Increase in cash and cash   equivalents	0.3			107.0			1.0			—			108.3
Cash and cash equivalents at   beginning of period	—			0.3			2.8			—			3.1
Cash and cash equivalents at     end of period	$	0.3		$	107.3		$	3.8		$	—		$	111.4

Condensed Consolidating Statements of Cash Flow for the Nine Months Ended September 30, 2015

(Millions)

	Parent Guarantor			Subsidiary Issuer			Non-guarantor Subsidiaries			Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Net cash provided by (used in)     operating activities	$	20.4		$	(99.5	)	$	509.3		$	—		$	430.2
INVESTING ACTIVITIES:
Capital expenditures	—			—			(241.1		)	—			(241.1		)
Proceeds from sale of operating assets	—			—			0.3			—			0.3
Proceeds from other recoveries	—			—			6.2			—			6.2
Advances to affiliates, net	(60.9		)	(276.5		)	(71.4		)	408.8			—
Net cash (used in) provided by     investing activities	(60.9		)	(276.5		)	(306.0		)	408.8			(234.6		)
FINANCING ACTIVITIES:
Proceeds from long-term debt, net of     issuance cost	—			247.1			—			—			247.1
Repayment of borrowings from long-term     debt and term loan	—			—			(725.0		)	—			(725.0		)
Proceeds from borrowings on revolving     credit agreement	—			—			980.0			—			980.0
Repayment of borrowings on revolving     credit agreement, including financing     fees	—			(3.6		)	(735.0		)	—			(738.6		)
Principal payment of capital lease     obligation	—			—			(0.3		)	—			(0.3		)
Advances from affiliates, net	0.6			132.3			276.5			(408.8		)	0.6
Distributions paid	(76.0		)	—			—			—			(76.0		)
Proceeds from sale of common units	113.1			—			—			—			113.1
Capital contributions from general partner	2.3			—			—			—			2.3
Net cash provided by (used in)     financing activities	40.0			375.8			(203.8		)	(408.8		)	(196.8		)
Decrease in cash and cash     equivalents	(0.5		)	(0.2		)	(0.5		)	—			(1.2		)
Cash and cash equivalents at     beginning of period	0.5			1.8			4.3			—			6.6
Cash and cash equivalents at     end of period	$	—		$	1.6		$	3.8		$	—		$	5.4