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Other assets and liabilities F.2. Inventories (Details) - USD ($)
$ in Millions
Dec. 31, 2018
Dec. 31, 2017
Subclassifications of assets, liabilities and equities [abstract]    
Telephone and equipment $ 26 $ 28
SIM cards 4 6
IRUs 3 3
Other 6 9
Inventory $ 39 $ 45