Benefit Plans - Components of Net Postemployment Costs (Details) - Postemployment Benefit Plans - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 6	$ 6	$ 5
Interest cost	5	4	4
Amortization of net gains	(4)	(3)	(3)
Net periodic benefit cost	$ 7	$ 7	$ 6