Revenues (Contract liabilities) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Contract balances
Deferred contract revenues, recorded in other current liabilities	$ 138	$ 100
Deferred contract revenues, recorded in other long-term liabilities	346	429
Total contract liabilities	$ 484	$ 529	$ 505	$ 486