Description of Business and Summary of Significant Accounting Policies - Trade Receivables (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Changes in Allowances for Uncollectible Accounts
Beginning balance	$ 43	$ 43	$ 42
Provision charged to expense	5	3	7
Write-offs, net of recoveries	(3)	(6)	(6)
Acquisitions and divestitures	0	0	1
Foreign currency translation	(1)	3	(1)
Ending balance	21	43	43
Adoption of new revenue recognition guidance
Changes in Allowances for Uncollectible Accounts
Beginning balance	$ 23	0	0
Ending balance		$ 23	$ 0