Pension and Other Postretirement Benefits - Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Pension benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 5	$ 1	$ 10	$ 1
Interest cost	28	1	54	2
Expected return on plan assets	(45)	(1)	(85)	(2)
Settlement	31	1	61	2
Amortization of prior service benefit	(1)	0	(1)	0
Net periodic benefit cost	73	2	94	3
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	55	0	55	0
Other postretirement benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	1	0	2	0
Interest cost	4	0	8	0
Settlement	1	0	3	0
Amortization of prior service benefit	0	0	(1)	0
Net periodic benefit cost	$ 6	$ 0	$ 12	$ 0