Note 3 - Regulated Operations (Details) - Bad Debt Rider (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Benchmark	$ 63gas_CustomerRefundLiabilityBenchmark	$ 63gas_CustomerRefundLiabilityBenchmark	$ 63gas_CustomerRefundLiabilityBenchmark
Actual Bad Debt	35us-gaap_ProvisionForDoubtfulAccounts	21us-gaap_ProvisionForDoubtfulAccounts	23us-gaap_ProvisionForDoubtfulAccounts
Total Refund	28gas_CustomerRefundLiability	42gas_CustomerRefundLiability	40gas_CustomerRefundLiability
Amount to be Refunded in 2015	16us-gaap_CustomerRefundLiabilityCurrent	17us-gaap_CustomerRefundLiabilityCurrent
Amount to be Refunded in 2016	12
Refunded in 2013 [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Amount Refunded			24
Refunded in 2014 [Member]
Valuation Allowance for Impairment of Recognized Servicing Assets [Line Items]
Amount Refunded		$ 25	$ 16

Amount refundable to customers.

No definition available.

Name:	gas_CustomerRefundLiability
Namespace Prefix:	gas_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the customer refund liability benchmark.

+ References

No definition available.

+ Details

Name:	gas_CustomerRefundLiabilityBenchmark
Namespace Prefix:	gas_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of refund payments made to customers during the period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 605

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 13.A.4(a))

-URI http://asc.fasb.org/extlink&oid=27012821&loc=d3e214044-122780

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

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 13

-Section A

-Paragraph a

-Subsection 4

+ Details

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

- Definition

Current regulatory liabilities generally represent obligations to make refunds to customers for various reasons including overpayment.

+ References

No definition available.

+ Details

Name:	us-gaap_CustomerRefundLiabilityCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Noncurrent regulatory liabilities generally represent obligations to make refunds to customers for various reasons including overpayment.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.24)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_CustomerRefundLiabilityNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of expense related to write-down of receivables to the amount expected to be collected. Includes, but is not limited to, accounts receivable and notes receivable.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (a)

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

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.5)

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

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 5

-Article 5

+ Details

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

- Details

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

- Details

Name:	gas_TimePeriodAxis=gas_RefundedIn2014Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	gas_TimePeriodAxis=gas_RefundedInTwoThousandThirteenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: