Pledged Assets (Narrative) (Details)	Dec. 31, 2018
Pledged Assets [Abstract]
Risk Of Repurchase Agreement To Stockholders Equity	4.00%

Risk Of Repurchase Agreement To Stockholders Equity

No definition available.

Name:	agnc_RiskOfRepurchaseAgreementToStockholdersEquity
Namespace Prefix:	agnc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant