Pension and Postretirement Benefit Plans - Narrative (Details) - Funded - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Aug. 31, 2015	Dec. 31, 2018	Dec. 31, 2017
United States
Benefit Plan Information
Original percentage medical inflation indexation by company in year	3.00%
Revised percentage medical inflation indexation by company in year	1.50%
Qualified and Non-qualified Pension Benefits
Benefit Plan Information
Company contributions year to date		$ 366	$ 964
Qualified and Non-qualified Pension Benefits | United States
Benefit Plan Information
Company contributions year to date		254	852
Qualified and Non-qualified Pension Benefits | International
Benefit Plan Information
Company contributions year to date		112	112
Postretirement Benefits
Benefit Plan Information
Company contributions year to date		$ 4	$ 3