Discontinued Operations (Income Statement Disclosures) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Net Revenues
Transportation and storage revenues			$ 260.3		$ 561.4
Other revenues			55.6		94.3
Total Sales Revenues			315.9		655.7
Less: Cost of sales (excluding depreciation and amortization)			0.1		0.2
Net Revenues			315.8		655.5
Operating Expenses
Operation and maintenance			204.3		369.3
Depreciation and amortization			33.9		66.4
Gain on sale of assets			(8.3)		(13.6)
Other taxes			18.8		38.0
Total Operating Expenses			248.7		460.1
Equity Earnings in Unconsolidated Affiliates			13.7		29.1
Operating Income from Discontinued Operations			80.8		224.5
Other Income (Deductions)
Interest expense, net			(18.9)		(37.1)
Other, net			3.5		7.2
Total Other Income (Deductions)			(15.4)		(29.9)
Income (Loss) from Discontinued Operations before Income Taxes			65.4		194.6
Income Taxes			20.0		66.4
Income (Loss) from Discontinued Operations - net of taxes		$ (0.1)	45.4	$ (0.1)	128.2
Columbia Pipeline Group Operations | Discontinued Operations, Spinoff
Net Revenues
Transportation and storage revenues			260.3		561.4
Other revenues			55.6		94.3
Total Sales Revenues			315.9		655.7
Less: Cost of sales (excluding depreciation and amortization)			0.1		0.2
Net Revenues			315.8		655.5
Operating Expenses
Operation and maintenance	[1]		204.3		369.3
Depreciation and amortization			33.9		66.4
Gain on sale of assets			(8.3)		(13.6)
Other taxes			18.8		38.0
Total Operating Expenses			248.7		460.1
Equity Earnings in Unconsolidated Affiliates			13.7		29.1
Operating Income from Discontinued Operations			80.8		224.5
Other Income (Deductions)
Interest expense, net			(18.9)		(37.1)
Other, net			4.2		7.8
Total Other Income (Deductions)			(14.7)		(29.3)
Income (Loss) from Discontinued Operations before Income Taxes			66.1		195.2
Income Taxes			20.3		66.7
Income (Loss) from Discontinued Operations - net of taxes			45.8		128.5
Corporate and Other | Discontinued Operations, Spinoff
Net Revenues
Transportation and storage revenues			0.0		0.0
Other revenues			0.0		0.0
Total Sales Revenues			0.0		0.0
Less: Cost of sales (excluding depreciation and amortization)			0.0		0.0
Net Revenues			0.0		0.0
Operating Expenses
Operation and maintenance			0.0		0.0
Depreciation and amortization			0.0		0.0
Gain on sale of assets			0.0		0.0
Other taxes			0.0		0.0
Total Operating Expenses			0.0		0.0
Equity Earnings in Unconsolidated Affiliates			0.0		0.0
Operating Income from Discontinued Operations			0.0		0.0
Other Income (Deductions)
Interest expense, net			0.0		0.0
Other, net			(0.7)		(0.6)
Total Other Income (Deductions)			(0.7)		(0.6)
Income (Loss) from Discontinued Operations before Income Taxes			(0.7)		(0.6)
Income Taxes			(0.3)		(0.3)
Income (Loss) from Discontinued Operations - net of taxes			$ (0.4)		$ (0.3)

[1] Includes approximately $28.7 million and $48.9 million of transaction costs related to the Separation for the three and six months ended June 30, 2015, respectively.