Significant Accounting Policies - Reconciliation of Cash, Cash Equivalents and Restriced Cash (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 831	$ 1,273	$ 1,275
Cash, cash equivalents, restricted cash and restricted cash equivalents	856	1,328	$ 1,275	$ 1,277
Other current assets [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash and cash equivalents	13	42
Other noncurrent assets [Member]
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash and cash equivalents	$ 12	$ 13