Property, Plant, and Equipment (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010
Property, Plant, and Equipment
Total property, plant, and equipment, at cost	$ 19,082		$ 17,795
Accumulated depreciation and amortization	(6,502)		(6,041)
Property, plant and equipment - net	12,580		11,754
Natural gas gathering and processing facilities [Member] | Nonregulated [Member]
Property, Plant, and Equipment
Estimated Useful Life (years), Minimum	5	[1]
Estimated Useful Life (years), Maximum	40	[1]
Total property, plant, and equipment, at cost	6,435		6,134
Natural gas transmission facilities [Member] | Regulated [Member]
Property, Plant, and Equipment
Property, Plant, and Equipment, Depreciation Rate, Minimum	0.01%	[1]
Property, Plant, and Equipment, Depreciation Rate, Maximum	6.67%	[1]
Total property, plant, and equipment, at cost	9,593		9,066
Construction in Progress [Member] | Regulated [Member]
Property, Plant, and Equipment
Total property, plant, and equipment, at cost	199	[2]	240	[2]
Construction in Progress [Member] | Nonregulated [Member]
Property, Plant, and Equipment
Total property, plant, and equipment, at cost	648	[2]	223	[2]
Other Capitalized Property Plant and Equipment [Member] | Regulated [Member]
Property, Plant, and Equipment
Property, Plant, and Equipment, Depreciation Rate, Minimum	0.01%	[1]
Property, Plant, and Equipment, Depreciation Rate, Maximum	33.33%	[1]
Total property, plant, and equipment, at cost	1,391		1,359
Other Capitalized Property Plant and Equipment [Member] | Nonregulated [Member]
Property, Plant, and Equipment
Estimated Useful Life (years), Minimum	3	[1]
Estimated Useful Life (years), Maximum	45	[1]
Total property, plant, and equipment, at cost	$ 816		$ 773

[1] Estimated useful life and depreciation rates are presented as of December 31, 2011. Depreciation rates for regulated assets are prescribed by the FERC.

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