Employee Benefit Plans - Postemployment Plan (Details) - Postemployment Plan - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Net service cost	$ 14	$ 10
Interest cost	1	1
Amortization of prior service benefit	(1)	(1)
Amortization of actuarial gain	(1)	0
Net benefit cost	$ 13	$ 10