Revenues (Contract liabilities) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Contract balances
Deferred contract revenues, recorded in other current liabilities	$ 102	$ 133
Deferred contract revenues, recorded in other long-term liabilities	282	323
Total contract liabilities	$ 384	$ 456	$ 519	$ 529