Asset Acquisition, Consideration Transferred

No definition available.

Name:	agr_AssetAcquisitionConsiderationTransferred
Namespace Prefix:	agr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Asset Acquisition, Recognized Identifiable Assets Acquired and Liabilities Assumed, Derivative Liabilities

+ References

No definition available.

+ Details

Name:	agr_AssetAcquisitionRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedDerivativeLiabilities
Namespace Prefix:	agr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Asset Acquisition, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Liabilities

+ References

No definition available.

+ Details

Name:	agr_AssetAcquisitionRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedOtherLiabilities
Namespace Prefix:	agr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Asset Acquisition, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment

+ References

No definition available.

+ Details

Name:	agr_AssetAcquisitionRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedPropertyPlantandEquipment
Namespace Prefix:	agr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Proposed Wind Farm and Electricity Transmission Project Capacity

+ References

No definition available.

+ Details

Name:	agr_ProposedWindFarmandElectricityTransmissionProjectCapacity
Namespace Prefix:	agr_
Data Type:	num:powerItemType
Balance Type:	na
Period Type:	duration

- Definition

The membership interests in tax equity financing arrangements sold to third-party investors which are reflected as a financing obligation to the third party, current obligation.

+ References

No definition available.

+ Details

Name:	agr_TaxEquityFinancingArrangementsNoncurrent
Namespace Prefix:	agr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=109237563&loc=d3e33749-111570

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 25
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8813-108599

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.12)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

The carrying amount of the consolidated Variable Interest Entity's assets included in the reporting entity's statement of financial position.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (bb)
-URI http://asc.fasb.org/extlink&oid=118582676&loc=d3e5710-111685

+ Details

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

- Definition

The carrying amount of the consolidated Variable Interest Entity's liabilities included in the reporting entity's statement of financial position.

+ References

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Details

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

- Details

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

Variable Interest Entities (Detail) $ in Millions	Jun. 28, 2019 USD ($) MW	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Variable Interest Entity [Line Items]
Assets of variable interest entities (VIEs)		$ 1,178	$ 876
Liabilities of variable interest entities (VIEs)		60	50
Equity method investments of variable interest entities (VIEs)		505	366
Patriot Wind Farm LLC
Variable Interest Entity [Line Items]
Proposed wind farm and electricity transmission project capacity (MW) \| MW	226
Purchase price	$ 320
Business combination, property, plant, and equipment	348
Business combination, derivative liabilities	26
Business combination, other liabilities	2
Tax equity financing arrangements - VIEs	$ 128
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Equity method investments of variable interest entities (VIEs)		$ 98	$ 101