Property, Plant, and Equipment (Details) (USD $) In Millions, unless otherwise specified					12 Months Ended																				12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Natural gas gathering and processing facilities [Member] Nonregulated [Member]	Dec. 31, 2011 Natural gas gathering and processing facilities [Member] Nonregulated [Member]	Dec. 31, 2012 Natural gas gathering and processing facilities [Member] Nonregulated [Member] Minimum [Member]		Dec. 31, 2012 Natural gas gathering and processing facilities [Member] Nonregulated [Member] Maximum [Member]		Dec. 31, 2012 Natural gas transmission facilities [Member] Regulated [Member]		Dec. 31, 2011 Natural gas transmission facilities [Member] Regulated [Member]	Dec. 31, 2012 Construction in Progress [Member] Regulated [Member]		Dec. 31, 2011 Construction in Progress [Member] Regulated [Member]		Dec. 31, 2012 Construction in Progress [Member] Nonregulated [Member]		Dec. 31, 2011 Construction in Progress [Member] Nonregulated [Member]		Dec. 31, 2012 Other Capitalized Property Plant and Equipment [Member] Regulated [Member]		Dec. 31, 2011 Other Capitalized Property Plant and Equipment [Member] Regulated [Member]	Dec. 31, 2012 Other Capitalized Property Plant and Equipment [Member] Nonregulated [Member]	Dec. 31, 2011 Other Capitalized Property Plant and Equipment [Member] Nonregulated [Member]	Dec. 31, 2012 Other Capitalized Property Plant and Equipment [Member] Nonregulated [Member] Minimum [Member]		Dec. 31, 2012 Other Capitalized Property Plant and Equipment [Member] Nonregulated [Member] Maximum [Member]
Property, Plant, and Equipment
Property, Plant and Equipment, Useful Life					5 years	[1]	40 years	[1]																	3 years	[1]	45 years	[1]
Property, Plant, and Equipment, Depreciation Rate, Minimum									1.01%	[1]										0.18%	[1]
Property, Plant, and Equipment, Depreciation Rate, Maximum									6.82%	[1]										33.33%	[1]
Total property, plant, and equipment, at cost	$ 22,546	$ 19,082	$ 7,727	$ 6,435					$ 9,963		$ 9,593	$ 337	[2]	$ 199	[2]	$ 1,997	[2]	$ 648	[2]	$ 1,419		$ 1,391	$ 1,103	$ 816
Accumulated depreciation and amortization	(7,079)	(6,502)
Property, plant and equipment - net	$ 15,467	$ 12,580

[1] Estimated useful life and depreciation rates are presented as of December 31, 2012. Depreciation rates for regulated assets are prescribed by the FERC.

[2] Construction in progress balances not yet subject to depreciation.