Intangible Assets and Goodwill, Significant Intangible Assets (Details) (USD $) In Millions, unless otherwise specified					12 Months Ended							12 Months Ended		12 Months Ended				12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Customer relationship intangibles [Member]	Dec. 31, 2012 Customer relationship intangibles [Member] State Line Gathering [Member]		Dec. 31, 2012 Customer relationship intangibles [Member] Fairplay Gathering [Member]		Dec. 31, 2012 Customer relationship intangibles [Member] Fairplay Processing [Member]		Dec. 31, 2012 Customer relationship intangibles [Member] State Line and Fairplay [Member]	Dec. 31, 2012 Customer relationship intangibles [Member] San Juan Gathering [Member]	Dec. 31, 2012 Customer relationship intangibles [Member] Offshore Pipelines and Platforms [Member]	Dec. 31, 2012 Customer relationship intangibles [Member] Offshore Pipelines and Platforms [Member] Minimum [Member]	Dec. 31, 2012 Customer relationship intangibles [Member] Offshore Pipelines and Platforms [Member] Maximum [Member]	Dec. 31, 2012 Customer relationship intangibles [Member] Encinal [Member]	Dec. 31, 2012 Contract-based intangibles [Member]	Dec. 31, 2012 Contract-based intangibles [Member] San Juan Gathering [Member]	Dec. 31, 2012 Contract-based intangibles [Member] Jonah Gas Gathering [Member]	Dec. 31, 2012 Contract-based intangibles [Member] Shell Processing Agreement [Member]
Identifiable intangible assets [Abstract]
Gross Value	$ 2,616.8	$ 2,646.6			$ 675.0	[1]	$ 116.6	[1]	$ 103.4	[2]	$ 895.0
Accumulated Amortization	(1,050.0)	(990.4)			(52.8)	[1]	(18.2)	[1]	(16.1)	[2]	(87.1)
Carrying Value	$ 1,566.8	$ 1,656.2	$ 1,841.7	$ 1,250.0	$ 622.2	[1]	$ 98.4	[1]	$ 87.3	[2]	$ 807.9	$ 173.4	$ 65.4			$ 64.1	$ 317.9	$ 56.7	$ 96.1	$ 72.7
Finite-Lived Intangible Asset, Useful Life					27 years		23 years		23 years			35 years		11 years	33 years	20 years		20 years	40 years	20 years

[1] These natural gas gathering customer relationship intangible assets are a component of our Onshore Natural Gas Pipelines & Services business segment.

[2] The Fairplay natural gas processing customer relationship intangible assets are a component of our NGL Pipelines & Services business segment.