Name:	agnc_GrossAmountOfRecognizedAssetsLiabilities
Namespace Prefix:	agnc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

No definition available.

Name:	agnc_GrossAmountOffsetintheConsolidatedBalanceSheets
Namespace Prefix:	agnc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Gross Amounts of Cash Collateral Not Offset on the Balance Sheet

No definition available.

Name:	agnc_GrossAmountsofCashCollateralNotOffsetontheBalanceSheet
Namespace Prefix:	agnc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Fair value of financial asset or liability or other contract elected not to be offset against an obligation to return collateral or right to receive collateral pledged under a master netting arrangement.

No definition available.

Name:	agnc_GrossAmountsofFinancialInstrumentsNotOffsetontheBalanceSheet
Namespace Prefix:	agnc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Net amount after deducting gross amounts not offset on the balance sheet from net amount of assets (liabilities) presented on the balance sheet.

No definition available.

Name:	agnc_NetAmountAfterDeductingGrossAmountsNotOffsetontheBalanceSheetFromNetAmountofAssetsLiabilitiesPresentedontheBalanceSheet
Namespace Prefix:	agnc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Fair value after effects of master netting arrangements, of a financial asset or liability or other contract and the contract can be net settled by means outside the contract or delivery of an asset or liability.

No definition available.

Name:	agnc_NetAmountofAssetsLiabilitiesPresentedontheBalanceSheet
Namespace Prefix:	agnc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

[Line Items] for Offsetting Assets and Liabilities [Table]

No definition available.

Name:	agnc_OffsettingAssetsAndLiabilitiesLineItems
Namespace Prefix:	agnc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_AssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_SwaptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_DerivativeInstrumentRiskAxis=agnc_TBAAndForwardSettlingSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_DerivativeInstrumentRiskAxis=agnc_ReverseRepurchaseAgreementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_LiabilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_RepurchaseAgreementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: