| 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 |
