Note 10 - Segment Information (Detail) - Intersegment Reporting (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011		Dec. 31, 2011
Operating revenues from external parties	$ 686		$ 375		$ 2,090		$ 1,253
Intercompany revenues	0	[1]	0	[1]	0	[1]	0	[1]
Total operating revenues	686		375		2,090		1,253
Operating expenses
Cost of goods sold	240		134		959		589
Operation and maintenance	218		119		463		248
Depreciation and amortization	102		42		206		83
Nicor merger expenses	3		8		13		10
Taxes other than income taxes	32		12		96		25
Total operating expenses	595		315		1,737		955
Operating income (loss)	91		60		353		298
Other income	9		2		13		3
EBIT	100		62		366		301
Identifiable and total assets	13,274	[2]	7,217	[2]	13,274	[2]	7,217	[2]	13,913	[3]
Goodwill	1,813		418		1,813		418		1,813
Capital expenditures	179		102		350		196
Distribution Operations [Member]
Operating revenues from external parties	449		236		1,443		741
Intercompany revenues	41	[1]	41	[1]	87	[1]	79	[1]
Total operating revenues	490		277		1,530		820
Operating expenses
Cost of goods sold	131		70		660		338
Operation and maintenance	152		89		325		179
Depreciation and amortization	86		36		174		72
Nicor merger expenses	0		0		0		0
Taxes other than income taxes	25		9		82		18
Total operating expenses	394		204		1,241		607
Operating income (loss)	96		73		289		213
Other income	4		1		5		2
EBIT	100		74		294		215
Identifiable and total assets	10,829	[2]	5,592	[2]	10,829	[2]	5,592	[2]	11,020	[3]
Goodwill	1,586		404		1,586		404		1,586
Capital expenditures	146		87		268		167
Retail Operations [Member]
Operating revenues from external parties	136		117		399		407
Intercompany revenues	0	[1]	0	[1]	0	[1]	0	[1]
Total operating revenues	136		117		399		407
Operating expenses
Cost of goods sold	93		100		259		301
Operation and maintenance	25		15		57		35
Depreciation and amortization	3		0		7		1
Nicor merger expenses	0		0		0		0
Taxes other than income taxes	1		1		2		1
Total operating expenses	122		116		325		338
Operating income (loss)	14		1		74		69
Other income	0		0		0		0
EBIT	14		1		74		69
Identifiable and total assets	452	[2]	189	[2]	452	[2]	189	[2]	501	[3]
Goodwill	124		0		124		0		124
Capital expenditures	2		0		4		1
Wholesale Services [Member]
Operating revenues from external parties	7		9		71		62
Intercompany revenues	0	[1]	0	[1]	0	[1]	0	[1]
Total operating revenues	7		9		71		62
Operating expenses
Cost of goods sold	4		1		34		4
Operation and maintenance	11		12		24		28
Depreciation and amortization	0		1		1		1
Nicor merger expenses	0		0		0		0
Taxes other than income taxes	1		0		2		1
Total operating expenses	16		14		61		34
Operating income (loss)	(9)		(5)		10		28
Other income	0		0		0		0
EBIT	(9)		(5)		10		28
Identifiable and total assets	895	[2]	1,038	[2]	895	[2]	1,038	[2]	1,214	[3]
Goodwill	2		0		2		0		2
Capital expenditures	0		1		0		1
Midstream Operations [Member]
Operating revenues from external parties	18		11		34		41
Intercompany revenues	0	[1]	0	[1]	0	[1]	0	[1]
Total operating revenues	18		11		34		41
Operating expenses
Cost of goods sold	7		2		12		23
Operation and maintenance	4		4		9		8
Depreciation and amortization	4		2		6		4
Nicor merger expenses	0		0		0		0
Taxes other than income taxes	2		1		3		2
Total operating expenses	17		9		30		37
Operating income (loss)	1		2		4		4
Other income	1		0		1		0
EBIT	2		2		5		4
Identifiable and total assets	685	[2]	476	[2]	685	[2]	476	[2]	635	[3]
Goodwill	16		14		16		14		16
Capital expenditures	17		8		59		15
Cargo Shipping [Member]
Operating revenues from external parties	80		0		164		0
Intercompany revenues	0	[1]	0	[1]	0	[1]	0	[1]
Total operating revenues	80		0		164		0
Operating expenses
Cost of goods sold	51		0		101		0
Operation and maintenance	26		0		54		0
Depreciation and amortization	6		0		12		0
Nicor merger expenses	0		0		0		0
Taxes other than income taxes	1		0		3		0
Total operating expenses	84		0		170		0
Operating income (loss)	(4)		0		(6)		0
Other income	3		0		6		0
EBIT	(1)		0		0		0
Identifiable and total assets	471	[2]	0	[2]	471	[2]	0	[2]	481	[3]
Goodwill	77		0		77		0		77
Capital expenditures	1		0		1		0
All Other Segments [Member]
Operating revenues from external parties	(4)	[4]	2	[4]	(21)	[4]	2	[4]
Intercompany revenues	(41)	[1],[4]	(41)	[1],[4]	(87)	[1],[4]	(79)	[1],[4]
Total operating revenues	(45)	[4]	(39)	[4]	(108)	[4]	(77)	[4]
Operating expenses
Cost of goods sold	(46)	[4]	(39)	[4]	(107)	[4]	(77)	[4]
Operation and maintenance	0	[4]	(1)	[4]	(6)	[4]	(2)	[4]
Depreciation and amortization	3	[4]	3	[4]	6	[4]	5	[4]
Nicor merger expenses	3	[4]	8	[4]	13	[4]	10	[4]
Taxes other than income taxes	2	[4]	1	[4]	4	[4]	3	[4]
Total operating expenses	(38)	[4]	(28)	[4]	(90)	[4]	(61)	[4]
Operating income (loss)	(7)	[4]	(11)	[4]	(18)	[4]	(16)	[4]
Other income	1	[4]	1	[4]	1	[4]	1	[4]
EBIT	(6)	[4]	(10)	[4]	(17)	[4]	(15)	[4]
Identifiable and total assets	(58)	[2],[4]	(78)	[2],[4]	(58)	[2],[4]	(78)	[2],[4]	62	[3],[5]
Goodwill	8	[4]	0	[4]	8	[4]	0	[4]	8	[5]
Capital expenditures	$ 13	[4]	$ 6	[4]	$ 18	[4]	$ 12	[4]

[1] 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 $49 million and $137 million for the three and six months ended June 30, 2012 and $102 million and $249 million for the three and six months ended June 30, 2011.

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

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

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