Employee Benefit Plans - Net Period Cost (Details) - Pension Benefits - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Components of net periodic benefit cost [Abstract]
Service cost	$ 7	$ 4
Interest cost	20	19
Expected return on plan assets	(31)	(25)
Amortization of net actuarial loss	8	4
Net periodic cost	$ 4	$ 2