Revenues - Significant Movements in Deferred Revenue Balances (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Revenue from Contract with Customer [Abstract]
Beginning balance	$ 419	$ 336
Amounts billed but not recognized as revenues	327	297
Revenues recognized related to the opening balance of deferred revenue	357	268
Ending balance	$ 389	$ 365