Summary of Significant Accounting Policies - Recently Issued Accounting Guidance Not Yet Adopted (Details) - Accounting Standards Update 2016-01 [Member] $ in Millions	Dec. 31, 2016 USD ($)
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Current carrying value of certain limited partnership interests to be reported at fair value upon adoption of ASU 2016-01	$ 260
Restatement Adjustment [Member] \| Shareholders' Equity [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Impact of new guidance on equity if adopted	$ 60

Amount of cumulative effect of the change in accounting principle or new accounting pronouncement on retained earnings or other components of equity or net assets in the statement of financial position if implemented as of the implementation date.

No definition available.

Name:	ci_NewAccountingPronouncementOrChangeInAccountingPrincipleCumulativeEfa
Namespace Prefix:	ci_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant