Document and Entity Information
9 Months Ended
Sep. 30, 2017
Document And Entity Information [Abstract]  
Entity Registrant Name Cobalt International Energy, Inc.
Entity Central Index Key 0001471261
Document Type 10-Q
Document Period End Date Sep. 30, 2017
Amendment Flag false
Current Fiscal Year End Date --12-31
Trading Symbol CIE
Entity Filer Category Accelerated Filer
Entity Common Stock, Shares Outstanding 29,916,693
Document Fiscal Year Focus 2017
Document Fiscal Period Focus Q3