Summary of Significant Accounting Policies and Other Matters - Change in Unbilled Contract and Unearned Revenues (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2019	Jan. 01, 2018
Unbilled contract revenue
Beginning balance	$ 29	$ 58
Additions	86	144
Subtractions	86	173
Ending balance	29	29
Unearned revenue
Beginning balance	20	87
Additions	1	38
Subtractions	4	105
Ending balance	$ 17	$ 20
Contracts with customer, revenue recognized, amount outstanding end of last period			$ 4	$ 50