Organization (Details)	12 Months Ended
Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Required distribution of taxable net income on a annual basis	90.00%
Intended annual distribution of taxable net income	100.00%

Intended Annual Distribution of Taxable Net Income

No definition available.

Name:	agnc_IntendedAnnualDistributionofTaxableNetIncome
Namespace Prefix:	agnc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration