Leases - Operating and Finance Lease Right of Use ("ROU") Assets and Lease Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Operating leases:
Operating lease ROU assets	$ 552	$ 536
Accrued expenses and other liabilities	152	166
Other non-current liabilities	491	465
Total operating lease liabilities	643	631
Finance leases:
Property and equipment, gross	98	110
Accumulated depreciation	(46)	(23)
Property and equipment, net	52	87
Short-term debt	18	27
Long-term debt	36	61
Total finance lease liabilities	$ 54	$ 88
Balance sheet location of current operating lease liabilities	ci:AccruedExpensesAndOtherLiabilities	ci:AccruedExpensesAndOtherLiabilities
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