Guarantee of Securities of Subsidiaries (Tables)

9 Months Ended

Sep. 30, 2017

Condensed Financial Information of Parent Company Only Disclosure [Abstract]

Condensed Consolidating Balance Sheet

The Partnership has provided the following condensed consolidating financial information in accordance with Regulation S-X Rule 3-10, Financial Statements of Guarantors and Issuers of Guaranteed Securities Registered or Being Registered.

Condensed Consolidating Balance Sheets as of September 30, 2017

(Millions)

Assets	Parent Guarantor		Subsidiary Issuer		Non-guarantor Subsidiaries		Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Cash and cash equivalents	$	0.4	$	15.1	$	7.1	$	—		$	22.6
Receivables	—		—		108.2		—			108.2
Receivables - affiliate	—		—		6.9		(6.9		)	—
Gas and liquids stored underground	—		—		5.6		—			5.6
Prepayments	0.4		—		19.4		—			19.8
Advances to affiliates	—		1.4		22.4		(23.8		)	—
Other current assets	—		—		8.2		(1.2		)	7.0
Total current assets	0.8		16.5		177.8		(31.9		)	163.2
Investment in consolidated subsidiaries	2,602.8		6,665.8		—		(9,268.6		)	—
Property, plant and equipment, gross	0.6		—		10,674.1		—			10,674.7
Less–accumulated depreciation    and amortization	0.6		—		2,542.5		—			2,543.1
Property, plant and equipment, net	—		—		8,131.6		—			8,131.6
Advances to affiliates – noncurrent	2,082.4		886.4		373.4		(3,342.2		)	—
Other noncurrent assets	—		3.4		464.1		(0.2		)	467.3
Total other assets	2,082.4		889.8		837.5		(3,342.4		)	467.3
Total Assets	$	4,686.0	$	7,572.1	$	9,146.9	$	(12,642.9	)	$	8,762.1

Liabilities and Partners' Capital	Parent Guarantor		Subsidiary Issuer		Non-guarantor Subsidiaries		Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Payables	$	0.1	$	0.2	$	87.6	$	—		$	87.9
Payable to affiliates	1.5		—		6.9		(6.9		)	1.5
Advances from affiliates	—		22.4		1.4		(23.8		)	—
Other current liabilities	0.2		29.9		174.6		(1.4		)	203.3
Total current liabilities	1.8		52.5		270.5		(32.1		)	292.7
Long-term debt and capital lease     obligation	—		2,461.0		1,124.7		—			3,585.7
Payable to affiliate - noncurrent	16.0		—		—		—			16.0
Advances from affiliates - noncurrent	—		2,455.8		886.4		(3,342.2		)	—
Other noncurrent liabilities	—		—		199.5		—			199.5
Total other liabilities and deferred     credits	16.0		2,455.8		1,085.9		(3,342.2		)	215.5
Total partners' capital	4,668.2		2,602.8		6,665.8		(9,268.6		)	4,668.2
Total Liabilities and Partners' Capital	$	4,686.0	$	7,572.1	$	9,146.9	$	(12,642.9	)	$	8,762.1

Condensed Consolidating Balance Sheets as of December 31, 2016

(Millions)

Assets	Parent  Guarantor		Subsidiary Issuer		Non-guarantor Subsidiaries		Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Cash and cash equivalents	$	0.6	$	1.8	$	2.2	$	—		$	4.6
Receivables	—		—		139.8		—			139.8
Receivables - affiliate	—		—		7.0		(7.0		)	—
Gas and liquids stored underground	—		—		1.3		—			1.3
Prepayments	0.4		—		17.3		—			17.7
Advances to affiliates	—		72.9		102.7		(175.6		)	—
Other current assets	—		—		13.9		(3.1		)	10.8
Total current assets	1.0		74.7		284.2		(185.7		)	174.2
Investment in consolidated subsidiaries	2,423.2		6,653.6		—		(9,076.8		)	—
Property, plant and equipment, gross	0.6		—		10,326.7		—			10,327.3
Less–accumulated depreciation    and amortization	0.6		—		2,333.2		—			2,333.8
Property, plant and equipment, net	—		—		7,993.5		—			7,993.5
Advances to affiliates – noncurrent	2,125.0		435.0		229.3		(2,789.3		)	—
Other noncurrent assets	—		3.3		466.8		—			470.1
Total other assets	2,125.0		438.3		696.1		(2,789.3		)	470.1
Total Assets	$	4,549.2	$	7,166.6	$	8,973.8	$	(12,051.8	)	$	8,637.8

Liabilities and Partners' Capital	Parent Guarantor		Subsidiary Issuer		Non-guarantor Subsidiaries		Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Payables	$	0.9	$	0.2	$	136.4	$	—		$	137.5
Payable to affiliates	1.4		—		7.0		(7.0		)	1.4
Advances from affiliates	—		102.7		72.9		(175.6		)	—
Other current liabilities	—		21.8		175.3		(3.1		)	194.0
Total current liabilities	2.3		124.7		391.6		(185.7		)	332.9
Long-term debt and capital lease     obligation	—		2,264.4		1,293.6		—			3,558.0
Payable to affiliate - noncurrent	16.0		—		—		—			16.0
Advances from affiliates - noncurrent	—		2,354.3		435.0		(2,789.3		)	—
Other noncurrent liabilities	—		—		200.0		—			200.0
Total other liabilities and deferred     credits	16.0		2,354.3		635.0		(2,789.3		)	216.0
Total partners' capital	4,530.9		2,423.2		6,653.6		(9,076.8		)	4,530.9
Total Liabilities and Partners' Capital	$	4,549.2	$	7,166.6	$	8,973.8	$	(12,051.8	)	$	8,637.8

Condensed Consolidating Statements of Income

Condensed Consolidating Statements of Income for the Three Months Ended September 30, 2017

(Millions)

	Parent Guarantor			Subsidiary Issuer			Non-guarantor Subsidiaries			Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Operating Revenues:
Transportation	$	—		$	—		$	295.4		$	(22.5	)	$	272.9
Parking and lending	—			—			4.3			—			4.3
Storage	—			—			18.9			—			18.9
Other	—			—			4.4			—			4.4
Total operating revenues	—			—			323.0			(22.5		)	300.5
Operating Costs and Expenses:
Fuel and transportation	—			—			31.5			(22.5		)	9.0
Operation and maintenance	—			—			49.0			—			49.0
Administrative and general	(0.3		)	—			26.6			—			26.3
Other operating costs and expenses	0.4			—			105.0			—			105.4
Total operating costs and expenses	0.1			—			212.1			(22.5		)	189.7
Operating (loss) income	(0.1		)	—			110.9			—			110.8
Other Deductions (Income):
Interest expense	—			32.2			8.8			—			41.0
Interest (income) expense - affiliates, net	(12.4		)	11.0			1.4			—			—
Equity in earnings of subsidiaries	(57.5		)	(100.7		)	—			158.2			—
Miscellaneous other income, net	—			—			(0.3		)	—			(0.3		)
Total other (income) deductions	(69.9		)	(57.5		)	9.9			158.2			40.7
Income (loss) before income taxes	69.8			57.5			101.0			(158.2		)	70.1
Income taxes	—			—			0.3			—			0.3
Net income (loss)	$	69.8		$	57.5		$	100.7		$	(158.2	)	$	69.8

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 Nine Months Ended September 30, 2017

(Millions)

	Parent Guarantor			Subsidiary Issuer			Non-guarantor Subsidiaries			Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Operating Revenues:
Transportation	$	—		$	—		$	936.5		$	(66.3	)	$	870.2
Parking and lending	—			—			17.8			(0.2		)	17.6
Storage	—			—			62.2			—			62.2
Other	—			—			35.1			—			35.1
Total operating revenues	—			—			1,051.6			(66.5		)	985.1
Operating Costs and Expenses:
Fuel and transportation	—			—			109.2			(66.5		)	42.7
Operation and maintenance	—			—			141.0			—			141.0
Administrative and general	(0.3		)	—			95.4			—			95.1
Other operating costs and expenses	0.5			—			363.0			—			363.5
Total operating costs and expenses	0.2			—			708.6			(66.5		)	642.3
Operating (loss) income	(0.2		)	—			343.0			—			342.8
Other Deductions (Income):
Interest expense	—			97.6			33.5			—			131.1
Interest (income) expense - affiliates, net	(34.6		)	30.1			4.5			—			—
Interest income	—			(0.2		)	(0.1		)	—			(0.3		)
Equity in earnings of subsidiaries	(178.4		)	(305.9		)	—			484.3			—
Miscellaneous other income, net	—			—			(1.7		)	—			(1.7		)
Total other (income) deductions	(213.0		)	(178.4		)	36.2			484.3			129.1
Income (loss) before income taxes	212.8			178.4			306.8			(484.3		)	213.7
Income taxes	—			—			0.9			—			0.9
Net income (loss)	$	212.8		$	178.4		$	305.9		$	(484.3	)	$	212.8

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 deductions     (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 Comprehensive Income

Condensed Consolidating Statements of Comprehensive Income for the Three Months Ended September 30, 2017

(Millions)

	Parent Guarantor		Subsidiary Issuer		Non-guarantor Subsidiaries		Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Net income (loss)	$	69.8	$	57.5	$	100.7	$	(158.2	)	$	69.8
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	0.1		0.1		0.1		(0.2		)	0.1
Total Comprehensive Income (Loss)	$	70.5	$	58.2	$	101.0	$	(159.2	)	$	70.5

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 Nine Months Ended September 30, 2017

(Millions)

	Parent Guarantor			Subsidiary Issuer			Non-guarantor Subsidiaries		Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Net income (loss)	$	212.8		$	178.4		$	305.9	$	(484.3	)	$	212.8
Other comprehensive income (loss):
Loss on cash flow hedge	(1.5		)	(1.5		)	—		1.5			(1.5		)
Reclassification adjustment transferred     to Net income from cash flow hedges	1.9			1.9			0.5		(2.4		)	1.9
Pension and other postretirement     benefit costs	0.8			0.8			0.8		(1.6		)	0.8
Total Comprehensive Income (Loss)	$	214.0		$	179.6		$	307.2	$	(486.8	)	$	214.0

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 Cash Flows

Condensed Consolidating Statements of Cash Flow for the Nine Months Ended September 30, 2017

(Millions)

	Parent Guarantor			Subsidiary  Issuer			Non-guarantor Subsidiaries			Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Net cash provided by (used in)     operating activities	$	33.8		$	(117.0	)	$	586.4		$	—		$	503.2
INVESTING ACTIVITIES:
Capital expenditures	—			—			(496.0		)	—			(496.0		)
Proceeds from sale of operating assets	—			—			63.7			—			63.7
Advances to affiliates, net	42.6			(398.5		)	(377.4		)	733.3			—
Net cash provided by (used in)     investing activities	42.6			(398.5		)	(809.7		)	733.3			(432.3		)
FINANCING ACTIVITIES:
Proceeds from long-term debt, net of     issuance cost	—			494.0			—			—			494.0
Repayment of borrowings from long-term     debt	—			(300.0		)	(275.0		)	—			(575.0		)
Proceeds from borrowings on revolving     credit agreement	—			—			505.0			—			505.0
Repayment of borrowings on revolving     credit agreement	—			—			(400.0		)	—			(400.0		)
Principal payment of capital lease     obligation	—			—			(0.3		)	—			(0.3		)
Advances from affiliates, net	0.1			334.8			398.5			(733.3		)	0.1
Distributions paid	(76.7		)	—			—			—			(76.7		)
Net cash (used in) provided by     financing activities	(76.6		)	528.8			228.2			(733.3		)	(52.9		)
(Decrease) increase in cash and cash   equivalents	(0.2		)	13.3			4.9			—			18.0
Cash and cash equivalents at   beginning of period	0.6			1.8			2.2			—			4.6
Cash and cash equivalents at     end of period	$	0.4		$	15.1		$	7.1		$	—		$	22.6

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