Pension Plans and Other Postretirement Benefits - Net Periodic Benefit Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Settlement losses	$ 0	$ 0	$ 187
Pension Plan
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Interest cost	225	25	20
Expected return on plan assets	(357)	(33)	(20)
Amortization of net actuarial loss	1	2	21
Settlement losses	0	0	187
Net periodic benefit cost (income)	$ (131)	$ (6)	$ 208