Pension and Other Postretirement Benefits - Change in Plan Benefit Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension
Change in benefit obligation:
Benefit obligation at January 1	$ 2,429	$ 2,661
Service cost	52	60	$ 63
Interest cost	78	72	72
Plan participants’ contributions	2	2
Amendments	0	9
Actuarial (gain) loss	295	(162)
Transfer to liabilities held for sale	(2)	0
Benefits paid	(156)	(165)
Medicare subsidy received	0	0
Liabilities from other immaterial plans	0	5
Foreign currency translation	33	(53)
Benefit obligation at December 31	2,731	2,429	2,661
Other Postretirement Benefits
Change in benefit obligation:
Benefit obligation at January 1	511	546
Service cost	7	8	9
Interest cost	20	18	19
Plan participants’ contributions	12	12
Amendments	0	0
Actuarial (gain) loss	61	(35)
Transfer to liabilities held for sale	0	0
Benefits paid	(42)	(40)
Medicare subsidy received	1	2
Liabilities from other immaterial plans	0	0
Foreign currency translation	0	0
Benefit obligation at December 31	$ 570	$ 511	$ 546