Note 10 - Segment Information (Details) - Intersegment Reporting (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012		Dec. 31, 2012
Segment Reporting Information [Line Items]
Operating revenues	$ 904		$ 686		$ 2,613		$ 2,090
Operating expenses
Cost of goods sold	407		240		1,380		959
Operation and maintenance	233		218		492		463
Depreciation and amortization	109		102		216		206
Taxes other than income taxes	44		32		115		96
Total operating expenses	793		595		2,203		1,737
Nicor merger expenses			3	[1]			13	[1]
Gain on sale of Compass Energy	11				11
Operating income (loss)	122		91		421		353
Other income	7		9		12		13
EBIT	129		100		433		366
Identifiable and total assets	13,795	[2]	13,229	[2]	13,795	[2]	13,229	[2]	14,141	[3]
Goodwill	1,883		1,813		1,883		1,813		1,837
Capital expenditures	170		179		318		350
External Parties [Member] | Distribution Operations [Member]
Segment Reporting Information [Line Items]
Operating revenues	615		449		1,879		1,443
External Parties [Member] | Retail Operations [Member]
Segment Reporting Information [Line Items]
Operating revenues	165		136		467		399
External Parties [Member] | Wholesale Services [Member]
Segment Reporting Information [Line Items]
Operating revenues	21		7		60		71
External Parties [Member] | Midstream Operations [Member]
Segment Reporting Information [Line Items]
Operating revenues	15		18		39		34
External Parties [Member] | Cargo Shipping [Member]
Segment Reporting Information [Line Items]
Operating revenues	88		80		175		164
External Parties [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		[4]	(4)	[4]	(7)	[4]	(21)	[4]
External Parties [Member]
Segment Reporting Information [Line Items]
Operating revenues	904		686		2,613		2,090
Intersegment Eliminations [Member] | Distribution Operations [Member]
Segment Reporting Information [Line Items]
Operating revenues	43	[5]	41	[5]	98	[5]	87	[5]
Intersegment Eliminations [Member] | Retail Operations [Member]
Segment Reporting Information [Line Items]
Operating revenues		[5]		[5]		[5]		[5]
Intersegment Eliminations [Member] | Wholesale Services [Member]
Segment Reporting Information [Line Items]
Operating revenues		[5]		[5]		[5]		[5]
Intersegment Eliminations [Member] | Midstream Operations [Member]
Segment Reporting Information [Line Items]
Operating revenues		[5]		[5]		[5]		[5]
Intersegment Eliminations [Member] | Cargo Shipping [Member]
Segment Reporting Information [Line Items]
Operating revenues		[5]		[5]		[5]		[5]
Intersegment Eliminations [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	(43)	[4],[5]	(41)	[4],[5]	(98)	[4],[5]	(87)	[4],[5]
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenues		[5]		[5]		[5]		[5]
Distribution Operations [Member]
Segment Reporting Information [Line Items]
Operating revenues	658		490		1,977		1,530
Operating expenses
Cost of goods sold	266		131		1,031		660
Operation and maintenance	159		152		344		325
Depreciation and amortization	90		86		180		174
Taxes other than income taxes	38		25		102		82
Total operating expenses	553		394		1,657		1,241
Nicor merger expenses				[1]				[1]
Operating income (loss)	105		96		320		289
Other income	4		4		7		5
EBIT	109		100		327		294
Identifiable and total assets	11,166	[2]	10,784	[2]	11,166	[2]	10,784	[2]	11,320	[3]
Goodwill	1,640		1,586		1,640		1,586		1,640
Capital expenditures	158		146		295		268
Retail Operations [Member]
Segment Reporting Information [Line Items]
Operating revenues	165		136		467		399
Operating expenses
Cost of goods sold	115		93		310		259
Operation and maintenance	32		25		63		57
Depreciation and amortization	5		3		10		7
Taxes other than income taxes	1		1		2		2
Total operating expenses	153		122		385		325
Nicor merger expenses				[1]				[1]
Operating income (loss)	12		14		82		74
EBIT	12		14		82		74
Identifiable and total assets	641	[2]	452	[2]	641	[2]	452	[2]	511	[3]
Goodwill	168		124		168		124		122
Capital expenditures	3		2		4		4
Wholesale Services [Member]
Segment Reporting Information [Line Items]
Operating revenues	21		7		60		71
Operating expenses
Cost of goods sold	10		4		20		34
Operation and maintenance	10		11		23		24
Depreciation and amortization	1				1		1
Taxes other than income taxes			1		1		2
Total operating expenses	21		16		45		61
Nicor merger expenses				[1]				[1]
Gain on sale of Compass Energy	11				11
Operating income (loss)	11		(9)		26		10
EBIT	11		(9)		26		10
Identifiable and total assets	1,008	[2]	895	[2]	1,008	[2]	895	[2]	1,218	[3]
Goodwill			2				2
Midstream Operations [Member]
Segment Reporting Information [Line Items]
Operating revenues	15		18		39		34
Operating expenses
Cost of goods sold	4		7		16		12
Operation and maintenance	6		4		12		9
Depreciation and amortization	4		4		8		6
Taxes other than income taxes	2		2		3		3
Total operating expenses	16		17		39		30
Nicor merger expenses				[1]				[1]
Operating income (loss)	(1)		1				4
Other income	1		1		2		1
EBIT			2		2		5
Identifiable and total assets	715	[2]	685	[2]	715	[2]	685	[2]	720	[3]
Goodwill	14		16		14		16		14
Capital expenditures	4		17		8		59
Cargo Shipping [Member]
Segment Reporting Information [Line Items]
Operating revenues	88		80		175		164
Operating expenses
Cost of goods sold	54		51		107		101
Operation and maintenance	30		26		58		54
Depreciation and amortization	5		6		10		12
Taxes other than income taxes	2		1		3		3
Total operating expenses	91		84		178		170
Nicor merger expenses				[1]				[1]
Operating income (loss)	(3)		(4)		(3)		(6)
Other income	2		3		4		6
EBIT	(1)		(1)		1
Identifiable and total assets	462	[2]	471	[2]	462	[2]	471	[2]	464	[3]
Goodwill	61		77		61		77		61
Capital expenditures	2		1		3		1
Other Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	(43)	[4]	(45)	[4]	(105)	[4]	(108)	[4]
Operating expenses
Cost of goods sold	(42)	[4]	(46)	[4]	(104)	[4]	(107)	[4]
Operation and maintenance	(4)	[4]		[4]	(8)	[4]	(6)	[4]
Depreciation and amortization	4	[4]	3	[4]	7	[4]	6	[4]
Taxes other than income taxes	1	[4]	2	[4]	4	[4]	4	[4]
Total operating expenses	(41)	[4]	(38)	[4]	(101)	[4]	(90)	[4]
Nicor merger expenses			3	[1],[4]			13	[1],[4]
Gain on sale of Compass Energy		[4]				[4]
Operating income (loss)	(2)	[4]	(7)	[4]	(4)	[4]	(18)	[4]
Other income		[4]	1	[4]	(1)	[4]	1	[4]
EBIT	(2)	[4]	(6)	[4]	(5)	[4]	(17)	[4]
Identifiable and total assets	(197)	[2],[4]	(58)	[2],[4]	(197)	[2],[4]	(58)	[2],[4]	(92)	[3],[6]
Goodwill		[4]	8	[4]		[4]	8	[4]		[6]
Capital expenditures	$ 3	[4]	$ 13	[4]	$ 8	[4]	$ 18	[4]

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

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

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

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

[5] Intercompany revenues - wholesale services records its energy marketing and risk management revenues on a net basis and its total operating revenues include intercompany revenues of $103 million and $243 million for the three and six months ended June 30, 2013 and $49 million and $137 million for the three and six months ended June 30, 2012.

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