Segment Information Schedule of Assets Related to Balance Sheet (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Segment Reporting Information
Total assets	$ 8,521	$ 8,123
Gathering and Processing
Segment Reporting Information
Total assets	4,491	4,210
Natural Gas Transportation [Member]
Segment Reporting Information
Total assets	1,202	1,232
NGL Services [Member]
Segment Reporting Information
Total assets	987	948
Contract Services [Member]
Segment Reporting Information
Total assets	1,761	1,672
Corporate and Others
Segment Reporting Information
Total assets	$ 80	$ 61