The aggregate cost of goods produced and sold and services rendered during the reporting period.

Name:	us-gaap_CostOfRevenue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Total costs of sales and operating expenses for the period.

+ References

+ Details

Name:	us-gaap_CostsAndExpenses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The current period expense charged against earnings on long-lived, physical assets not used in production, and which are not intended for resale, to allocate or recognize the cost of such assets over their useful lives; or to record the reduction in book value of an intangible asset over the benefit period of such asset; or to reflect consumption during the period of an asset that is not used in production.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 360

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

+ Details

Name:	us-gaap_DepreciationAndAmortization
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The net result for the period of deducting operating expenses from operating revenues.

+ References

No definition available.

+ Details

Name:	us-gaap_OperatingIncomeLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

+ Details

Name:	us-gaap_Revenues
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The aggregate total costs related to selling a firm's product and services, as well as all other general and administrative expenses. Direct selling expenses (for example, credit, warranty, and advertising) are expenses that can be directly linked to the sale of specific products. Indirect selling expenses are expenses that cannot be directly linked to the sale of specific products, for example telephone expenses, Internet, and postal charges. General and administrative expenses include salaries of non-sales personnel, rent, utilities, communication, etc.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.4)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 4

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 330

-SubTopic 10

-Section 30

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=34747878&loc=d3e3636-108311

+ Details

Name:	us-gaap_SellingGeneralAndAdministrativeExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of operating expense for taxes other than income taxes of regulated operation.

+ References

+ Details

Name:	us-gaap_UtilitiesOperatingExpenseTaxes
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_VariableInterestEntityLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=gas_SouthStarMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Note 10 - Non-wholly Owned Entities (Details) - SouthStar’s Revenues and Expenses (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Variable Interest Entity [Line Items]
Operating revenues	$ 1,445us-gaap_Revenues	$ 589us-gaap_Revenues	$ 889us-gaap_Revenues	$ 2,462us-gaap_Revenues	$ 1,218us-gaap_Revenues	$ 574us-gaap_Revenues	$ 805us-gaap_Revenues	$ 1,612us-gaap_Revenues	$ 5,385us-gaap_Revenues	$ 4,209us-gaap_Revenues	$ 3,562us-gaap_Revenues
Operating income	286us-gaap_OperatingIncomeLoss	78us-gaap_OperatingIncomeLoss	139us-gaap_OperatingIncomeLoss	592us-gaap_OperatingIncomeLoss	166us-gaap_OperatingIncomeLoss	70us-gaap_OperatingIncomeLoss	113us-gaap_OperatingIncomeLoss	290us-gaap_OperatingIncomeLoss	1,095us-gaap_OperatingIncomeLoss	639us-gaap_OperatingIncomeLoss	590us-gaap_OperatingIncomeLoss
Cost of goods sold									2,765us-gaap_CostOfRevenue	2,110us-gaap_CostOfRevenue	1,583us-gaap_CostOfRevenue
Operation and maintenance									939	887	816
Depreciation and amortization									380us-gaap_DepreciationAndAmortization	397us-gaap_DepreciationAndAmortization	394us-gaap_DepreciationAndAmortization
Taxes other than income taxes									208us-gaap_UtilitiesOperatingExpenseTaxes	187us-gaap_UtilitiesOperatingExpenseTaxes	159us-gaap_UtilitiesOperatingExpenseTaxes
Total operating expenses									4,292us-gaap_CostsAndExpenses	3,581us-gaap_CostsAndExpenses	2,972us-gaap_CostsAndExpenses
South Star [Member]
Variable Interest Entity [Line Items]
Operating revenues									866	687
Operating income									122	116
Cost of goods sold									645	491
Operation and maintenance									87	72
Depreciation and amortization									11	7
Taxes other than income taxes									1	1
Total operating expenses									$ 744	$ 571