Basis of Presentation (Schedule of Cash Activity) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash and cash equivalents	$ 1,324	$ 692	$ 1,258
Program cash	84	72	79
Restricted Cash	3		2
Total cash and cash equivalents, program and restricted cash	$ 1,411	$ 765	$ 1,339	$ 900