v3.8.0.1
Document and Entity Information - USD ($)
$ in Billions
12 Months Ended
Dec. 31, 2017
Jan. 31, 2018
Jun. 30, 2017
Document and Entity Information [Abstract]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Dec. 31, 2017    
Document Fiscal Year Focus 2017    
Document Fiscal Period Focus Q4    
Entity Registrant Name AGNC Investment Corp.    
Entity Central Index Key 0001423689    
Entity Filer Category Large Accelerated Filer    
Current Fiscal Year End Date --12-31    
Entity Common Stock, Shares Outstanding   391,316,840  
Trading Symbol AGNC    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Public Float     $ 6.3