Note 10 - Segment Information (Detail) - Segment Reporting (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012		Mar. 31, 2012
Identifiable and Total Assets	$ 13,940	[1]	$ 14,141	[2]	$ 13,239	[3]
Goodwill	1,883		1,837		1,813
Distribution Operations [Member]
Identifiable and Total Assets	11,258	[1]	11,320	[2]	10,785	[3]
Goodwill	1,640		1,640		1,586
Retail Operations [Member]
Identifiable and Total Assets	668	[1]	511	[2]	471	[3]
Goodwill	168		122		124
Wholesale Services [Member]
Identifiable and Total Assets	1,005	[1]	1,218	[2]	917	[3]
Goodwill					2
Midstream Operations [Member]
Identifiable and Total Assets	714	[1]	720	[2]	665	[3]
Goodwill	14		14		16
Cargo Shipping [Member]
Identifiable and Total Assets	459	[1]	464	[2]	477	[3]
Goodwill	61		61		77
All Other Segments [Member]
Identifiable and Total Assets	(164)	[1],[4]	(92)	[2],[5]	(76)	[3],[4]
Goodwill		[4]		[5]	$ 8	[4]

[1] Transaction expenses associated with the Nicor merger are shown separately to better compare year-over-year results.

[2] Identifiable assets are those assets used in each segment's operations.

[3] Identifiable assets are those used in each segment's operations.

[4] Our other segment's assets consist primarily of cash and cash equivalents and PP&E, and reflect the effect of intercompany eliminations.

[5] Our other segment's assets consist primarily of cash and cash equivalents and PP&E and reflect the effect of intercompany eliminations.