Supplementary Information for Certain Balance Sheet Accounts - Other non - Current Assets (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Prepayments and accrued income	$ 14	$ 14
Deferred contract costs	59	46
Deferred compensation plan assets	137	125
Deferred tax assets	71	59
Accounts receivable, net	17	20
Other investments	21	7
Insurance recovery receivables	102	86
Other non-current assets	120	110
Total other non-current assets	$ 541	$ 467