Accounting Policies - Restricted Cash (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Cash and Cash Equivalents	$ 1,006	$ 908	$ 917
Restricted Cash	32		63
Total Cash, Cash Equivalents and Restricted Cash	$ 1,038	$ 974	$ 980	$ 873