Pension and Other Benefit Programs - Components of Pension Plan Expense (Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
Interest cost	$ 26	$ 27	$ 27
Estimated return on plan assets	(29)	(44)	(44)
Amortization of loss	4	2	1
Aggregate pension expense (benefit)	$ 1	$ (15)	$ (16)