Employee Benefit Plans - Components of Net Periodic Benefit Cost (Benefit) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Pension Plan [Member]
Component of periodic benefit cost
Service cost	$ 1	$ 1
Interest cost	(32)	(39)
Expected return on plan assets	(54)	(57)
Amortization of prior service credit	0	0
Amortization of actuarial loss	(15)	(11)
Net periodic cost (benefit)	(6)	(6)
Other Postretirement Benefits Plan [Member]
Component of periodic benefit cost
Service cost	0	0
Interest cost	(2)	(2)
Expected return on plan assets	(1)	(1)
Amortization of prior service credit	(2)	(1)
Amortization of actuarial loss	(2)	(1)
Net periodic cost (benefit)	$ 1	$ 1