Note 10 - Segment Information (Detail) - Intersegment Reporting (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011		Dec. 31, 2011
Operating revenues from external parties	$ 614		$ 295		$ 2,704		$ 1,548
Intercompany revenues	0	[1]	0	[1]	0	[1]	0	[1]
Total operating revenues	614		295		2,704		1,548
Operating expenses
Cost of goods sold	215		112		1,174		701
Operation and maintenance	212		103		675		351
Depreciation and amortization	104		43		310		126
Taxes other than income taxes	27		11		123		36
Nicor merger expenses	2		2		15		12
Total operating expenses	560		271		2,297		1,226
Operating income (loss)	54		24		407		322
Other income	6		1		19		4
EBIT	60		25		426		326
Identifiable and total assets	13,595	[2]	7,459	[2]	13,595	[2]	7,459	[2]	13,913	[3]
Goodwill	1,817		418		1,817		418		1,813
Capital expenditures	219		96		569		292
Distribution Operations [Member]
Operating revenues from external parties	405		205		1,848		946
Intercompany revenues	37	[1]	34	[1]	124	[1]	113	[1]
Total operating revenues	442		239		1,972		1,059
Operating expenses
Cost of goods sold	107		47		767		385
Operation and maintenance	148		79		473		258
Depreciation and amortization	88		37		262		109
Taxes other than income taxes	21		8		103		26
Nicor merger expenses	0		0		0		0
Total operating expenses	364		171		1,605		778
Operating income (loss)	78		68		367		281
Other income	2		2		7		4
EBIT	80		70		374		285
Identifiable and total assets	11,062	[2]	5,673	[2]	11,062	[2]	5,673	[2]	11,020	[3]
Goodwill	1,591		404		1,591		404		1,586
Capital expenditures	189		82		457		249
Retail Operations [Member]
Operating revenues from external parties	118		98		517		505
Intercompany revenues	0	[1]	0	[1]	0	[1]	0	[1]
Total operating revenues	118		98		517		505
Operating expenses
Cost of goods sold	83		87		342		388
Operation and maintenance	26		15		83		50
Depreciation and amortization	3		1		10		2
Taxes other than income taxes	1		0		3		1
Nicor merger expenses	0		0		0		0
Total operating expenses	113		103		438		441
Operating income (loss)	5		(5)		79		64
Other income	0		0		0		0
EBIT	5		(5)		79		64
Identifiable and total assets	472	[2]	182	[2]	472	[2]	182	[2]	501	[3]
Goodwill	122		0		122		0		124
Capital expenditures	3		1		7		2
Wholesale Services [Member]
Operating revenues from external parties	(12)		(21)		59		41
Intercompany revenues	0	[1]	0	[1]	0	[1]	0	[1]
Total operating revenues	(12)		(21)		59		41
Operating expenses
Cost of goods sold	0		8		34		12
Operation and maintenance	11		7		35		35
Depreciation and amortization	0		0		1		1
Taxes other than income taxes	1		1		3		2
Nicor merger expenses	0		0		0		0
Total operating expenses	12		16		73		50
Operating income (loss)	(24)		(37)		(14)		(9)
Other income	1		0		1		0
EBIT	(23)		(37)		(13)		(9)
Identifiable and total assets	970	[2]	1,004	[2]	970	[2]	1,004	[2]	1,214	[3]
Goodwill	0		0		0		0		2
Capital expenditures	1		0		1		1
Midstream Operations [Member]
Operating revenues from external parties	22		11		56		52
Intercompany revenues	0	[1]	0	[1]	0	[1]	0	[1]
Total operating revenues	22		11		56		52
Operating expenses
Cost of goods sold	12		2		24		25
Operation and maintenance	4		4		13		12
Depreciation and amortization	4		2		10		6
Taxes other than income taxes	1		1		4		3
Nicor merger expenses	0		0		0		0
Total operating expenses	21		9		51		46
Operating income (loss)	1		2		5		6
Other income	0		0		1		0
EBIT	1		2		6		6
Identifiable and total assets	712	[2]	476	[2]	712	[2]	476	[2]	635	[3]
Goodwill	14		14		14		14		16
Capital expenditures	18		6		77		21
Cargo Shipping [Member]
Operating revenues from external parties	83		0		247		0
Intercompany revenues	0	[1]	0	[1]	0	[1]	0	[1]
Total operating revenues	83		0		247		0
Operating expenses
Cost of goods sold	51		0		152		0
Operation and maintenance	29		0		83		0
Depreciation and amortization	5		0		17		0
Taxes other than income taxes	1		0		4		0
Nicor merger expenses	0		0		0		0
Total operating expenses	86		0		256		0
Operating income (loss)	(3)		0		(9)		0
Other income	2		0		8		0
EBIT	(1)		0		(1)		0
Identifiable and total assets	482	[2]	0	[2]	482	[2]	0	[2]	481	[3]
Goodwill	90		0		90		0		77
Capital expenditures	1		0		2		0
All Other Segments [Member]
Operating revenues from external parties	(2)	[4]	2	[4]	(23)	[4]	4	[4]
Intercompany revenues	(37)	[1],[4]	(34)	[1],[4]	(124)	[1],[4]	(113)	[1],[4]
Total operating revenues	(39)	[4]	(32)	[4]	(147)	[4]	(109)	[4]
Operating expenses
Cost of goods sold	(38)	[4]	(32)	[4]	(145)	[4]	(109)	[4]
Operation and maintenance	(6)	[4]	(2)	[4]	(12)	[4]	(4)	[4]
Depreciation and amortization	4	[4]	3	[4]	10	[4]	8	[4]
Taxes other than income taxes	2	[4]	1	[4]	6	[4]	4	[4]
Nicor merger expenses	2	[4]	2	[4]	15	[4]	12	[4]
Total operating expenses	(36)	[4]	(28)	[4]	(126)	[4]	(89)	[4]
Operating income (loss)	(3)	[4]	(4)	[4]	(21)	[4]	(20)	[4]
Other income	1	[4]	(1)	[4]	2	[4]	0	[4]
EBIT	(2)	[4]	(5)	[4]	(19)	[4]	(20)	[4]
Identifiable and total assets	(103)	[2],[4]	124	[2],[4]	(103)	[2],[4]	124	[2],[4]	62	[3],[5]
Goodwill	0	[4]	0	[4]	0	[4]	0	[4]	8	[5]
Capital expenditures	$ 7	[4]	$ 7	[4]	$ 25		$ 19	[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 $93 million and $230 million for the three and nine months ended September 30, 2012 and $118 million and $367 million for the three and nine months ended September 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.