Revenue from Contracts with Customers - Contract Balances (Details) - USD ($) $ in Millions	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Accounts receivable, net	$ 377	$ 588
Contract assets	6	14
Deferred revenue, current	498	490	$ 490
Long-term deferred revenue	$ 82	$ 105	$ 105