Supplemental Cash Flow Information - Cash, Cash Equalivalents and Restricted Cash (Details) - USD ($) $ in Millions		Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Supplemental Cash Flow Elements [Abstract]
Cash and cash equivalents		$ 1,247	$ 1,687
Restricted cash	[1]	2	38
Cash, cash equivalents and restricted cash		$ 1,249	$ 1,725	$ 5,004	$ 3,015

[1] The restricted cash balance is included within other current assets on the consolidated balance sheets