Employee Benefit Plans - Components of Net Periodic Benefit Cost (Benefit) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1	$ 1	$ 3	$ 3
Interest cost	(31)	(40)	(95)	(119)
Expected return on plan assets	(53)	(57)	(161)	(170)
Amortization of prior service credit	0	0	0	0
Amortization of actuarial loss	(15)	(11)	(45)	(33)
Net periodic cost (benefit)	(6)	(5)	(18)	(15)
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost	(1)	(2)	(4)	(6)
Expected return on plan assets	0	(1)	(2)	(3)
Amortization of prior service credit	(2)	(2)	(5)	(5)
Amortization of actuarial loss	(2)	(1)	(5)	(4)
Net periodic cost (benefit)	$ 1	$ 0	$ 2	$ 2