Goodwill Goodwill (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013
Goodwill [Line Items]
Balance at December 31, 2012	$ 1,468
Contributed to Midstream Partnership	628
Balance at June 30, 2013	840
Natural Gas Distribution [Member]
Goodwill [Line Items]
Balance at December 31, 2012	746
Contributed to Midstream Partnership	0
Balance at June 30, 2013	746
Interstate Pipelines [Member]
Goodwill [Line Items]
Balance at December 31, 2012	579
Contributed to Midstream Partnership	579
Balance at June 30, 2013	0
Competitive Natural Gas Sales and Services [Member]
Goodwill [Line Items]
Balance at December 31, 2012	83
Contributed to Midstream Partnership	0
Balance at June 30, 2013	83
Field Services [Member]
Goodwill [Line Items]
Balance at December 31, 2012	49
Contributed to Midstream Partnership	49
Balance at June 30, 2013	0
Other Operations [Member]
Goodwill [Line Items]
Balance at December 31, 2012	11
Contributed to Midstream Partnership	0
Balance at June 30, 2013	$ 11