Investments - Commercial Mortgage Loan Maturities (Details)	Dec. 31, 2017
Investments:
Percentage of commercial mortage loan portfolio scheduled to mature in 2022 or thereafter	86.00%

Percentage of mortgage loans maturing after the fourth fiscal year following the latest fiscal year.

No definition available.

Name:	ci_MortgageLoansOnRealEstateMaturitiesAfterYearFourPercent
Namespace Prefix:	ci_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant