Retirement Benefits- Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure
Defined Benefit Plan, Service Cost	$ 1	$ 1	$ 0
Interest cost	3	2	1
Expected return on plan assets	(7)	(7)	(7)
Prior service credit amortization	24	14	1
Net periodic benefit cost	$ 21	$ 10	$ (5)