Note 2 - Significant Accounting Policies and Methods of Application (Details) - Changes in Amount of Goodwill (USD $) In Millions, unless otherwise specified	12 Months Ended			12 Months Ended				12 Months Ended				12 Months Ended		12 Months Ended				12 Months Ended				12 Months Ended		12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Distribution Operations [Member] Nicor Gas [Member]	Dec. 31, 2013 Distribution Operations [Member]	Dec. 31, 2012 Distribution Operations [Member]	Dec. 31, 2011 Distribution Operations [Member]	Dec. 31, 2012 Retail Operations [Member] Nicor Gas [Member]	Dec. 31, 2013 Retail Operations [Member]	Dec. 31, 2012 Retail Operations [Member]	Dec. 31, 2011 Retail Operations [Member]	Dec. 31, 2012 Wholesale Services [Member] Nicor Gas [Member]	Dec. 31, 2011 Wholesale Services [Member]	Dec. 31, 2012 Midstream Operations [Member] Nicor Gas [Member]	Dec. 31, 2013 Midstream Operations [Member]	Dec. 31, 2012 Midstream Operations [Member]	Dec. 31, 2011 Midstream Operations [Member]	Dec. 31, 2012 Cargo Shipping [Member] Nicor Gas [Member]	Dec. 31, 2013 Cargo Shipping [Member]	Dec. 31, 2012 Cargo Shipping [Member]	Dec. 31, 2011 Cargo Shipping [Member]	Dec. 31, 2012 Other Segments [Member] Nicor Gas [Member]	Dec. 31, 2011 Other Segments [Member]	Dec. 31, 2012 Nicor Gas [Member]
Goodwill [Line Items]
Goodwill	$ 1,888	$ 1,837	$ 1,813		$ 1,640	$ 1,640	$ 1,586		$ 173	$ 122	$ 124		$ 2		$ 14	$ 14	$ 16		$ 61	$ 61	$ 77		$ 8	$ 1,423
Adjustments to Goodwill	$ 51			$ 54				$ (2)	$ 51			$ (2)		$ (2)				$ (16)				$ (8)		$ 24