Intangible Assets and Goodwill, Significant Intangible Assets (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Identifiable intangible assets [Abstract]
Gross Value		$ 5,267.2	$ 5,273.0
Accumulated Amortization		(1,403.1)	(1,235.8)
Carrying Value		3,864.1	$ 4,037.2	$ 4,302.1
Customer relationship intangibles [Member]
Identifiable intangible assets [Abstract]
Carrying Value		3,500.0
Customer relationship intangibles [Member] | EFS Midstream [Member]
Identifiable intangible assets [Abstract]
Gross Value	[1]	1,409.8
Accumulated Amortization	[1]	(60.2)
Carrying Value	[1]	$ 1,349.6
Weighted Average Remaining Amortization Period	[1]	25 years 4 months 24 days
Cash flow projections discount rate		15.00%
Customer relationship intangibles [Member] | State Line and Fairplay [Member]
Identifiable intangible assets [Abstract]
Gross Value	[2]	$ 895.0
Accumulated Amortization	[2]	(150.9)
Carrying Value	[2]	$ 744.1
Weighted Average Remaining Amortization Period	[2]	30 years 2 months 12 days
Customer relationship intangibles [Member] | San Juan Gathering [Member]
Identifiable intangible assets [Abstract]
Gross Value	[3]	$ 331.3
Accumulated Amortization	[3]	(207.6)
Carrying Value	[3]	$ 123.7
Weighted Average Remaining Amortization Period	[3]	22 years 9 months 18 days
Customer relationship intangibles [Member] | Encinal [Member]
Identifiable intangible assets [Abstract]
Gross Value	[4]	$ 132.9
Accumulated Amortization	[4]	(92.9)
Carrying Value	[4]	$ 40.0
Weighted Average Remaining Amortization Period	[4]	10 years
Customer relationship intangibles [Member] | Oiltanking Partners L.P. [Member]
Identifiable intangible assets [Abstract]
Gross Value	[5]	$ 1,192.5
Accumulated Amortization	[5]	(32.5)
Carrying Value	[5]	$ 1,160.0
Weighted Average Remaining Amortization Period	[5]	27 years
Cash flow projections discount rate		6.50%
Contract-based intangibles [Member]
Identifiable intangible assets [Abstract]
Carrying Value		$ 367.6
Contract-based intangibles [Member] | Oiltanking Partners L.P. [Member]
Identifiable intangible assets [Abstract]
Gross Value		297.4
Carrying Value		$ 169.8
Weighted Average Remaining Amortization Period		4 years 7 months 6 days
Contract-based intangibles [Member] | Jonah Gas Gathering [Member]
Identifiable intangible assets [Abstract]
Carrying Value		$ 69.9
Weighted Average Remaining Amortization Period		25 years

[1] We acquired these intangible assets in connection with our acquisition of EFS Midstream in July 2015 (see Note 12 for additional information).

[2] These customer relationships are associated with our State Line and Fairplay Gathering Systems, which we acquired in 2010. The State Line system serves producers in the Haynesville and Bossier Shale supply basins and the Cotton Valley formation in Louisiana and eastern Texas. The Fairplay system serves producers in the Cotton Valley formation within Panola and Rusk counties in East Texas.

[3] These customer relationships are associated with our San Juan Gathering System, which serves producers in the San Juan Basin of northern New Mexico and southern Colorado. We acquired this intangible asset in 2004.

[4] These customer relationships are associated with our Encinal Gathering System, which serves producers in the Olmos and Wilcox formations in South Texas. We acquired this intangible asset in 2006.

[5] We acquired these intangible assets in connection with our acquisition of Oiltanking in October 2014 (see Note 12 for additional information).