Leases (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Operating leases:
Operating lease ROU assets	$ 530	$ 536
Accrued expenses and other current liabilities	160	166
Other non-current liabilities	461	465
Total operating lease liabilities	621	631
Finance leases:
Property and equipment, gross	99	110
Accumulated depreciation	(42)	(23)
Property and equipment, net	57	87
Short-term debt	20	27
Long-term debt	40	61
Total finance lease liabilities	$ 60	$ 88
Balance sheet location of non-current operating lease liabilities	us-gaap:OtherLiabilitiesNoncurrent	us-gaap:OtherLiabilitiesNoncurrent
Balance sheet location of non-current finance lease assets	us-gaap:PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization	us-gaap:PropertyPlantAndEquipmentAndFinanceLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization
Balance sheet location of current finance lease liabilities	us-gaap:DebtCurrent	us-gaap:DebtCurrent
Balance sheet location of non-current finance lease liabilities	us-gaap:LongTermDebtAndCapitalLeaseObligations	us-gaap:LongTermDebtAndCapitalLeaseObligations
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	ci:AccruedExpensesAndOtherLiabilities	ci:AccruedExpensesAndOtherLiabilities