Defined Contribution Plan, Employer Matching Contribution.

No definition available.

Name:	gas_DefinedContributionPlanEmployerMatchingContribution
Namespace Prefix:	gas_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Expected Savings Percentage of Medicare Liability.

+ References

No definition available.

+ Details

Name:	gas_ExpectedSavingsPercentageOfMedicareLiability
Namespace Prefix:	gas_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	gas_Note6EmployeeBenefitPlansDetailsLineItems
Namespace Prefix:	gas_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

1) For defined benefit pension plans, the benefit obligation is the projected benefit obligation, which is the actuarial present value as of a date of all benefits attributed by the pension benefit formula to employee service rendered prior to that date. 2) For other postretirement defined benefit plans, the benefit obligation is the accumulated postretirement benefit obligation, which is the actuarial present value of benefits attributed to employee service rendered to a particular date.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Projected Benefit Obligation

-URI http://asc.fasb.org/extlink&oid=6522206

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Accumulated Postretirement Benefit Obligation

-URI http://asc.fasb.org/extlink&oid=6503904

+ Details

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

- Definition

The increase in the fair value of plan assets from contributions made by the employer.

+ References

+ Details

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

- Definition

The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 340

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382

+ Details

Name:	us-gaap_RegulatoryAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Note 6 - Employee Benefit Plans (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Note 6 - Employee Benefit Plans (Details) [Line Items]
Expected Savings Percentage of Medicare Liability	12.00%
Regulatory Assets	$ 899	$ 1,089
Defined Contribution Plan, Employer Matching Contribution	16	14	7
Defined Benefit Welfare Benefits [Member] \| Other Postretirement Benefit Plan, Defined Benefit [Member]
Note 6 - Employee Benefit Plans (Details) [Line Items]
Regulatory Assets	108	215
Supplemental Employee Retirement Plan, Defined Benefit [Member]
Note 6 - Employee Benefit Plans (Details) [Line Items]
Defined Benefit Plan, Benefit Obligation	2	3
Pension Plan, Defined Benefit [Member]
Note 6 - Employee Benefit Plans (Details) [Line Items]
Defined Benefit Plan, Contributions by Employer		$ 40