v3.3.1.900
Document and Entity Information - shares
3 Months Ended
Mar. 31, 2016
Apr. 30, 2016
Document and Entity Information [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Mar. 31, 2016  
Document Fiscal Year Focus 2016  
Document Fiscal Period Focus Q1  
Entity Registrant Name American Capital Agency Corp  
Entity Central Index Key 0001423689  
Entity Filer Category Large Accelerated Filer  
Current Fiscal Year End Date --12-31  
Entity Common Stock, Shares Outstanding   330,999,538
Trading Symbol AGNC