Basis of Presentation (Schedule of Cash Activity) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash and cash equivalents	$ 576	$ 692	$ 679
Program cash	61	72	39
Restricted Cash	2		3
Total cash and cash equivalents, program and restricted cash	$ 639	$ 765	$ 721	$ 900