Document and Entity Information Document - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2019	Jan. 31, 2020	Jun. 30, 2019
Entity Information [Line Items]
Amendment Flag	false
Entity File Number	001-34057
Entity Registrant Name	AGNC INVESTMENT CORP.
Entity Address, Address Line One	2 Bethesda Metro Center, 12th Floor
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Shell Company	false
Entity Public Float			$ 7.4
Entity Common Stock, Shares Outstanding		540,943,011
Entity Filer Category	Large Accelerated Filer
Entity Incorporation, State or Country Code	DE
Document Transition Report	false
Document Annual Report	true
Document Type	10-K/A
Document Period End Date	Dec. 31, 2019
Entity Tax Identification Number	26-1701984
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Address, City or Town	Bethesda
Entity Address, State or Province	MD
Entity Address, Postal Zip Code	20814
City Area Code	301
Local Phone Number	968-9315
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Central Index Key	0001423689
Current Fiscal Year End Date	--12-31
Common Stock [Member]
Entity Information [Line Items]
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	AGNC
Security Exchange Name	NASDAQ
Depository shares each representing a 1/1,000th interest in a share of 7.000% Series C Fixed-to-Floating Rate Cumulative Redeemable Preferred Stock [Member]
Entity Information [Line Items]
Title of 12(b) Security	Depositary shares of 7.000% Series C Fixed-to-Floating Rate Cumulative Redeemable Preferred Stock
Trading Symbol	AGNCN
Security Exchange Name	NASDAQ
Depository shares each representing a 1/1,000th interest in a share of 6.875% Series D Fixed-to-Floating Rate Cumulative Redeemable Preferred Stock [Member]
Entity Information [Line Items]
Title of 12(b) Security	Depositary shares of 6.875% Series D Fixed-to-Floating Rate Cumulative Redeemable Preferred Stock
Trading Symbol	AGNCM
Security Exchange Name	NASDAQ
Depository shares each representing a 1/1000th interest in a share of 6.500% Series E Fixed-to-Floating Rate Cumulative Redeemable Preferred Stock [Member]
Entity Information [Line Items]
Title of 12(b) Security	Depositary shares of 6.50% Series E Fixed-to-Floating Rate Cumulative Redeemable Preferred Stock
Trading Symbol	AGNCO
Security Exchange Name	NASDAQ
Depositary shares each representing a 1/1000th interest in a share of 6.125% Series F Fixed-to-Floating Rate Cumulative Redeemable Preferred Stock [Member]
Entity Information [Line Items]
Title of 12(b) Security	Depositary shares of 6.125% Series F Fixed-to-Floating Rate Cumulative Redeemable Preferred Stock
Trading Symbol	AGNCP
Security Exchange Name	NASDAQ