Note 10 - Segment Information (Details) - Intersegment Reporting (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012		Dec. 31, 2012
Segment Reporting Information [Line Items]
Operating revenues	$ 675		$ 614		$ 3,288		$ 2,704
Cost of goods sold	229		215		1,609		1,174
Operation and maintenance	226		212		718		675
Depreciation and amortization	109		104		325		310
Taxes other than income taxes	29		27		144		123
Nicor merger expenses			2	[1]			15	[1]
Total operating expenses	593		560		2,796		2,297
Gain on sale of Compass Energy					11
Operating income (loss)	82		54		503		407
Other income	7		6		19		19
EBIT	89		60		522		426
Identifiable and total assets	13,904	[2]	13,503	[2]	13,904	[2]	13,503	[2]	14,141	[3]
Goodwill	1,883		1,817		1,883		1,817		1,837
Capital expenditures	217		219		535		569
External Parties [Member] | Distribution Operations [Member]
Segment Reporting Information [Line Items]
Operating revenues	420		405		2,299		1,848
External Parties [Member] | Retail Operations [Member]
Segment Reporting Information [Line Items]
Operating revenues	138		118		605		517
External Parties [Member] | Wholesale Services [Member]
Segment Reporting Information [Line Items]
Operating revenues	13		(12)		73		59
External Parties [Member] | Midstream Operations [Member]
Segment Reporting Information [Line Items]
Operating revenues	19		22		58		56
External Parties [Member] | Cargo Shipping [Member]
Segment Reporting Information [Line Items]
Operating revenues	89		83		264		247
External Parties [Member] | Other Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	(4)	[4]	(2)	[4]	(11)	[4]	(23)	[4]
External Parties [Member]
Segment Reporting Information [Line Items]
Operating revenues	675		614		3,288		2,704
Intersegment Eliminations [Member] | Distribution Operations [Member]
Segment Reporting Information [Line Items]
Operating revenues	36	[5]	37	[5]	134	[5]	124	[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	(36)	[4],[5]	(37)	[4],[5]	(134)	[4],[5]	(124)	[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	456		442		2,433		1,972
Cost of goods sold	111		107		1,142		767
Operation and maintenance	150		148		494		473
Depreciation and amortization	91		88		271		262
Taxes other than income taxes	22		21		124		103
Nicor merger expenses				[1]				[1]
Total operating expenses	374		364		2,031		1,605
Operating income (loss)	82		78		402		367
Other income	4		2		11		7
EBIT	86		80		413		374
Identifiable and total assets	11,300	[2]	10,970	[2]	11,300	[2]	10,970	[2]	11,320	[3]
Goodwill	1,640		1,591		1,640		1,591		1,640
Capital expenditures	200		189		495		457
Retail Operations [Member]
Segment Reporting Information [Line Items]
Operating revenues	138		118		605		517
Cost of goods sold	92		83		402		342
Operation and maintenance	31		26		94		83
Depreciation and amortization	6		3		16		10
Taxes other than income taxes	1		1		3		3
Nicor merger expenses				[1]				[1]
Total operating expenses	130		113		515		438
Operating income (loss)	8		5		90		79
EBIT	8		5		90		79
Identifiable and total assets	652	[2]	472	[2]	652	[2]	472	[2]	511	[3]
Goodwill	168		122		168		122		122
Capital expenditures	3		3		7		7
Wholesale Services [Member]
Segment Reporting Information [Line Items]
Operating revenues	13		(12)		73		59
Cost of goods sold	1				21		34
Operation and maintenance	13		11		36		35
Depreciation and amortization					1		1
Taxes other than income taxes	1		1		2		3
Nicor merger expenses				[1]				[1]
Total operating expenses	15		12		60		73
Gain on sale of Compass Energy					11
Operating income (loss)	(2)		(24)		24		(14)
Other income			1				1
EBIT	(2)		(23)		24		(13)
Identifiable and total assets	930	[2]	970	[2]	930	[2]	970	[2]	1,218	[3]
Capital expenditures			1				1
Midstream Operations [Member]
Segment Reporting Information [Line Items]
Operating revenues	19		22		58		56
Cost of goods sold	9		12		25		24
Operation and maintenance	5		4		17		13
Depreciation and amortization	5		4		13		10
Taxes other than income taxes	1		1		4		4
Nicor merger expenses				[1]				[1]
Total operating expenses	20		21		59		51
Operating income (loss)	(1)		1		(1)		5
Other income					2		1
EBIT	(1)		1		1		6
Identifiable and total assets	726	[2]	712	[2]	726	[2]	712	[2]	720	[3]
Goodwill	14		14		14		14		14
Capital expenditures	3		18		11		77
Cargo Shipping [Member]
Segment Reporting Information [Line Items]
Operating revenues	89		83		264		247
Cost of goods sold	55		51		162		152
Operation and maintenance	29		29		87		83
Depreciation and amortization	4		5		14		17
Taxes other than income taxes	2		1		5		4
Nicor merger expenses				[1]				[1]
Total operating expenses	90		86		268		256
Operating income (loss)	(1)		(3)		(4)		(9)
Other income	3		2		7		8
EBIT	2		(1)		3		(1)
Identifiable and total assets	464	[2]	482	[2]	464	[2]	482	[2]	464	[3]
Goodwill	61		90		61		90		61
Capital expenditures	6		1		9		2
Other Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	(40)	[4]	(39)	[4]	(145)	[4]	(147)	[4]
Cost of goods sold	(39)	[4]	(38)	[4]	(143)	[4]	(145)	[4]
Operation and maintenance	(2)	[4]	(6)	[4]	(10)	[4]	(12)	[4]
Depreciation and amortization	3	[4]	4	[4]	10	[4]	10	[4]
Taxes other than income taxes	2	[4]	2	[4]	6	[4]	6	[4]
Nicor merger expenses			2	[1],[4]			15	[1],[4]
Total operating expenses	(36)	[4]	(36)	[4]	(137)	[4]	(126)	[4]
Gain on sale of Compass Energy						[4]
Operating income (loss)	(4)	[4]	(3)	[4]	(8)	[4]	(21)	[4]
Other income		[4]	1	[4]	(1)	[4]	2	[4]
EBIT	(4)	[4]	(2)	[4]	(9)	[4]	(19)	[4]
Identifiable and total assets	(168)	[2],[4]	(103)	[2],[4]	(168)	[2],[4]	(103)	[2],[4]	(92)	[3],[4]
Goodwill		[4]		[4]		[4]		[4]		[4]
Capital expenditures	$ 5	[4]	$ 7	[4]	$ 13	[4]	$ 25	[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 $69 million and $312 million for the three and nine months ended September 30, 2013, respectively, and $93 million and $230 million for the three and nine months ended September 30, 2012, respectively.