Organization (Details) medical_member in Millions	Dec. 31, 2017 medical_member states counties
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of medical membership members \| medical_member	40.2
Number of counties in the Kansas City area the Company does not serve \| counties	30
Number of states in which the Company is licensed to conduct insurance operations \| states	50

Number of counties in a geographical region for which services are not provided.

No definition available.

Name:	antm_NumberOfCountiesInGeographicalRegionNotServed
Namespace Prefix:	antm_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant