| Document and Entity Information Document | Jul. 01, 2021 | Jun. 11, 2021 |
| Entity Information [Line Items] | ||
| Entity Central Index Key | 0001423689 | |
| Entity Emerging Growth Company | false | |
| Pre-commencement Issuer Tender Offer | false | |
| Pre-commencement Tender Offer | false | |
| Soliciting Material | false | |
| Written Communications | false | |
| City Area Code | 301 | |
| Local Phone Number | 968-9300 | |
| Entity Incorporation, State or Country Code | DE | |
| Entity File Number | 001-34057 | |
| Document Type | 8-K | |
| Document Period End Date | Jul. 1, 2021 | |
| Entity Registrant Name | AGNC INVESTMENT CORP. | |
| Entity Tax Identification Number | 26-1701984 | |
| Entity Address, Address Line One | 2 Bethesda Metro Center, 12th Floor | |
| Entity Address, City or Town | Bethesda | |
| Entity Address, State or Province | MD | |
| Entity Address, Postal Zip Code | 20814 | |
| Amendment Flag | false | |
| 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 |
