Guarantee of Securities of Subsidiaries (Tables)

6 Months Ended

Jun. 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 June 30, 2017

(Millions)

Assets	Parent Guarantor		Subsidiary Issuer		Non-guarantor Subsidiaries		Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Cash and cash equivalents	$	0.7	$	75.0	$	1.6	$	—		$	77.3
Receivables	—		—		112.8		—			112.8
Receivables - affiliate	—		—		6.9		(6.9		)	—
Gas and liquids stored underground	—		—		4.7		—			4.7
Prepayments	0.5		0.1		21.3		—			21.9
Advances to affiliates	—		2.4		10.1		(12.5		)	—
Other current assets	—		0.1		6.8		(1.5		)	5.4
Total current assets	1.2		77.6		164.2		(20.9		)	222.1
Investment in consolidated subsidiaries	2,544.6		6,829.8		—		(9,374.4		)	—
Property, plant and equipment, gross	0.6		—		10,498.0		—			10,498.6
Less–accumulated depreciation    and amortization	0.6		—		2,467.5		—			2,468.1
Property, plant and equipment, net	—		—		8,030.5		—			8,030.5
Advances to affiliates – noncurrent	2,095.3		508.7		283.3		(2,887.3		)	—
Other noncurrent assets	—		2.9		467.5		0.3			470.7
Total other assets	2,095.3		511.6		750.8		(2,887.0		)	470.7
Total Assets	$	4,641.1	$	7,419.0	$	8,945.5	$	(12,282.3	)	$	8,723.3

Liabilities and Partners' Capital	Parent Guarantor		Subsidiary Issuer		Non-guarantor Subsidiaries		Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Payables	$	0.3	$	0.2	$	127.8	$	—		$	128.3
Payable to affiliates	1.5		—		6.9		(6.9		)	1.5
Advances from affiliates	—		10.1		2.4		(12.5		)	—
Other current liabilities	—		25.3		155.5		(1.2		)	179.6
Total current liabilities	1.8		35.6		292.6		(20.6		)	309.4
Long-term debt and capital lease     obligation	—		2,460.2		1,114.3		—			3,574.5
Payable to affiliate - noncurrent	16.0		—		—		—			16.0
Advances from affiliates - noncurrent	—		2,378.6		508.7		(2,887.3		)	—
Other noncurrent liabilities	—		—		200.1		—			200.1
Total other liabilities and deferred     credits	16.0		2,378.6		708.8		(2,887.3		)	216.1
Total partners' capital	4,623.3		2,544.6		6,829.8		(9,374.4		)	4,623.3
Total Liabilities and Partners' Capital	$	4,641.1	$	7,419.0	$	8,945.5	$	(12,282.3	)	$	8,723.3

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 June 30, 2017

(Millions)

	Parent Guarantor			Subsidiary Issuer			Non-guarantor Subsidiaries			Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Operating Revenues:
Transportation	$	—		$	—		$	300.6		$	(21.9	)	$	278.7
Parking and lending	—			—			8.1			(0.2		)	7.9
Storage	—			—			19.9			—			19.9
Other	—			—			11.1			—			11.1
Total operating revenues	—			—			339.7			(22.1		)	317.6
Operating Costs and Expenses:
Fuel and transportation	—			—			36.6			(22.1		)	14.5
Operation and maintenance	—			—			51.6			—			51.6
Administrative and general	—			—			34.2			—			34.2
Other operating costs and expenses	—			—			150.1			—			150.1
Total operating costs and expenses	—			—			272.5			(22.1		)	250.4
Operating income	—			—			67.2			—			67.2
Other Deductions (Income):
Interest expense	—			32.4			11.5			—			43.9
Interest (income) expense - affiliates, net	(11.4		)	10.0			1.4			—			—
Interest income	—			(0.1		)	(0.1		)	—			(0.2		)
Equity in earnings of subsidiaries	(12.3		)	(54.6		)	—			66.9			—
Miscellaneous other income, net	—			—			(0.6		)	—			(0.6		)
Total other (income) deductions	(23.7		)	(12.3		)	12.2			66.9			43.1
Income (loss) before income taxes	23.7			12.3			55.0			(66.9		)	24.1
Income taxes	—			—			0.4			—			0.4
Net income (loss)	$	23.7		$	12.3		$	54.6		$	(66.9	)	$	23.7

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

(Millions)

	Parent Guarantor			Subsidiary Issuer			Non-guarantor Subsidiaries			Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Operating Revenues:
Transportation	$	—		$	—		$	291.7		$	(21.9	)	$	269.8
Parking and lending	—			—			5.4			(1.0		)	4.4
Storage	—			—			23.6			—			23.6
Other	—			—			8.5			—			8.5
Total operating revenues	—			—			329.2			(22.9		)	306.3
Operating Costs and Expenses:
Fuel and transportation	—			—			34.5			(22.9		)	11.6
Operation and maintenance	—			—			48.3			—			48.3
Administrative and general	—			—			35.5			—			35.5
Other operating costs and expenses	0.1			—			101.5			—			101.6
Total operating costs and expenses	0.1			—			219.8			(22.9		)	197.0
Operating (loss) income	(0.1		)	—			109.4			—			109.3
Other Deductions (Income):
Interest expense	—			30.4			15.0			—			45.4
Interest (income) expense - affiliates, net	(9.0		)	11.5			(2.5		)	—			—
Interest income	—			—			(0.1		)	—			(0.1		)
Equity in earnings of subsidiaries	(57.0		)	(98.9		)	—			155.9			—
Miscellaneous other deductions     (income), net	0.2			—			(2.1		)	—			(1.9		)
Total other (income) deductions	(65.8		)	(57.0		)	10.3			155.9			43.4
Income (loss) before income taxes	65.7			57.0			99.1			(155.9		)	65.9
Income taxes	—			—			0.2			—			0.2
Net income (loss)	$	65.7		$	57.0		$	98.9		$	(155.9	)	$	65.7

Condensed Consolidating Statements of Income for the Six Months Ended June 30, 2017

(Millions)

	Parent Guarantor			Subsidiary Issuer			Non-guarantor Subsidiaries			Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Operating Revenues:
Transportation	$	—		$	—		$	641.1		$	(43.8	)	$	597.3
Parking and lending	—			—			13.5			(0.2		)	13.3
Storage	—			—			43.3			—			43.3
Other	—			—			30.7			—			30.7
Total operating revenues	—			—			728.6			(44.0		)	684.6
Operating Costs and Expenses:
Fuel and transportation	—			—			77.7			(44.0		)	33.7
Operation and maintenance	—			—			92.0			—			92.0
Administrative and general	—			—			68.8			—			68.8
Other operating costs and expenses	0.1			—			258.0			—			258.1
Total operating costs and expenses	0.1			—			496.5			(44.0		)	452.6
Operating (loss) income	(0.1		)	—			232.1			—			232.0
Other Deductions (Income):
Interest expense	—			65.4			24.7			—			90.1
Interest (income) expense - affiliates, net	(22.2		)	19.1			3.1			—			—
Interest income	—			(0.2		)	(0.1		)	—			(0.3		)
Equity in earnings of subsidiaries	(120.9		)	(205.2		)	—			326.1			—
Miscellaneous other income, net	—			—			(1.4		)	—			(1.4		)
Total other (income) deductions	(143.1		)	(120.9		)	26.3			326.1			88.4
Income (loss) before income taxes	143.0			120.9			205.8			(326.1		)	143.6
Income taxes	—			—			0.6			—			0.6
Net income (loss)	$	143.0		$	120.9		$	205.2		$	(326.1	)	$	143.0

Condensed Consolidating Statements of Income for the Six Months Ended June 30, 2016

(Millions)

	Parent Guarantor			Subsidiary Issuer			Non-guarantor Subsidiaries			Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Operating Revenues:
Transportation	$	—		$	—		$	619.1		$	(43.4	)	$	575.7
Parking and lending	—			—			9.5			(1.0		)	8.5
Storage	—			—			44.6			—			44.6
Other	—			—			22.5			—			22.5
Total operating revenues	—			—			695.7			(44.4		)	651.3
Operating Costs and Expenses:
Fuel and transportation	—			—			76.3			(44.4		)	31.9
Operation and maintenance	—			—			91.7			—			91.7
Administrative and general	0.1			—			70.1			—			70.2
Other operating costs and expenses	0.2			—			206.4			—			206.6
Total operating costs and expenses	0.3			—			444.5			(44.4		)	400.4
Operating (loss) income	(0.3		)	—			251.2			—			250.9
Other Deductions (Income):
Interest expense	—			56.5			31.5			—			88.0
Interest (income) expense - affiliates, net	(17.9		)	23.5			(5.6		)	—			—
Interest income	—			—			(0.2		)	—			(0.2		)
Equity in earnings of subsidiaries	(149.3		)	(229.3		)	—			378.6			—
Miscellaneous other deductions     (income), net	0.2			—			(4.2		)	—			(4.0		)
Total other (income) deductions	(167.0		)	(149.3		)	21.5			378.6			83.8
Income (loss) before income taxes	166.7			149.3			229.7			(378.6		)	167.1
Income taxes	—			—			0.4			—			0.4
Net income (loss)	$	166.7		$	149.3		$	229.3		$	(378.6	)	$	166.7

Condensed Consolidating Statements Of Comprehensive Income

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

(Millions)

	Parent Guarantor		Subsidiary Issuer		Non-guarantor Subsidiaries		Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Net income (loss)	$	23.7	$	12.3	$	54.6	$	(66.9	)	$	23.7
Other comprehensive income (loss):
Reclassification adjustment transferred     to Net income from cash flow hedges	0.6		0.6		0.1		(0.7		)	0.6
Pension and other postretirement     benefit costs	0.4		0.4		0.4		(0.8		)	0.4
Total Comprehensive Income (Loss)	$	24.7	$	13.3	$	55.1	$	(68.4	)	$	24.7

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

(Millions)

	Parent Guarantor		Subsidiary Issuer		Non-guarantor Subsidiaries		Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Net income (loss)	$	65.7	$	57.0	$	98.9	$	(155.9	)	$	65.7
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	1.1		1.1		1.1		(2.2		)	1.1
Total Comprehensive Income (Loss)	$	67.4	$	58.7	$	100.2	$	(158.9	)	$	67.4

Condensed Consolidating Statements of Comprehensive Income for the Six Months Ended June 30, 2017

(Millions)

	Parent Guarantor			Subsidiary Issuer			Non-guarantor Subsidiaries		Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Net income (loss)	$	143.0		$	120.9		$	205.2	$	(326.1	)	$	143.0
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	1.3			1.3			0.3		(1.6		)	1.3
Pension and other postretirement     benefit costs	0.7			0.7			0.7		(1.4		)	0.7
Total Comprehensive Income (Loss)	$	143.5		$	121.4		$	206.2	$	(327.6	)	$	143.5

Condensed Consolidating Statements of Comprehensive Income for the Six Months Ended June 30, 2016

(Millions)

	Parent Guarantor		Subsidiary Issuer		Non-guarantor Subsidiaries		Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Net income (loss)	$	166.7	$	149.3	$	229.3	$	(378.6	)	$	166.7
Other comprehensive income (loss):
Reclassification adjustment transferred     to Net income from cash flow hedges	1.2		1.2		0.4		(1.6		)	1.2
Pension and other postretirement     benefit costs	1.7		1.7		1.7		(3.4		)	1.7
Total Comprehensive Income (Loss)	$	169.6	$	152.2	$	231.4	$	(383.6	)	$	169.6

Condensed Consolidating Statements of Cash Flows

Condensed Consolidating Statements of Cash Flow for the Six Months Ended June 30, 2017

(Millions)

	Parent Guarantor			Subsidiary  Issuer			Non-guarantor Subsidiaries			Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Net cash provided by (used in)     operating activities	$	21.4		$	(79.3	)	$	405.8		$	—		$	347.9
INVESTING ACTIVITIES:
Capital expenditures	—			—			(302.8		)	—			(302.8		)
Proceeds from sale of operating assets	—			—			64.8			—			64.8
Advances to affiliates, net	29.7			(3.2		)	8.6			(35.1		)	—
Net cash provided by (used in)     investing activities	29.7			(3.2		)	(229.4		)	(35.1		)	(238.0		)
FINANCING ACTIVITIES:
Proceeds from long-term debt, net of     issuance cost	—			494.0			—			—			494.0
Repayment of borrowings from long-term     debt	—			(300.0		)	—			—			(300.0		)
Proceeds from borrowings on revolving     credit agreement	—			—			160.0			—			160.0
Repayment of borrowings on revolving     credit agreement	—			—			(340.0		)	—			(340.0		)
Principal payment of capital lease     obligation	—			—			(0.2		)	—			(0.2		)
Advances from affiliates, net	0.1			(38.3		)	3.2			35.1			0.1
Distributions paid	(51.1		)	—			—			—			(51.1		)
Net cash (used in) provided by     financing activities	(51.0		)	155.7			(177.0		)	35.1			(37.2		)
Increase (decrease) in cash and cash   equivalents	0.1			73.2			(0.6		)	—			72.7
Cash and cash equivalents at   beginning of period	0.6			1.8			2.2			—			4.6
Cash and cash equivalents at     end of period	$	0.7		$	75.0		$	1.6		$	—		$	77.3

Condensed Consolidating Statements of Cash Flow for the Six Months Ended June 30, 2016

(Millions)

	Parent Guarantor			Subsidiary Issuer			Non-guarantor Subsidiaries			Eliminations			Consolidated Boardwalk Pipeline Partners, LP
Net cash provided by (used in)     operating activities	$	17.8		$	(73.3	)	$	360.2		$	—		$	304.7
INVESTING ACTIVITIES:
Capital expenditures	—			—			(259.0		)	—			(259.0		)
Proceeds from sale of operating assets	—			—			0.1			—			0.1
Advances to affiliates, net	33.6			(6.5		)	270.1			(297.2		)	—
Net cash provided by (used in)     investing activities	33.6			(6.5		)	11.2			(297.2		)	(258.9		)
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	—			—			(630.0		)	—			(630.0		)
Principal payment of capital lease     obligation	—			—			(0.2		)	—			(0.2		)
Advances from affiliates, net	0.1			(303.7		)	6.5			297.2			0.1
Distributions paid	(51.1		)	—			—			—			(51.1		)
Net cash (used in) provided by     financing activities	(51.0		)	235.4			(368.7		)	297.2			112.9
Increase in cash and cash     equivalents	0.4			155.6			2.7			—			158.7
Cash and cash equivalents at     beginning of period	—			0.3			2.8			—			3.1
Cash and cash equivalents at     end of period	$	0.4		$	155.9		$	5.5		$	—		$	161.8