Postretirement Benefit Plans (Summary of Amounts Recognized in Financial Statements) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in benefit obligation:
Benefit obligation at beginning of year		$ 914
Benefit obligation at end of year		1,008	$ 914
Change in plan assets:
Beginning Balance		567
Employer contributions	$ 19
Ending Balance		605	567
Unfunded status of the plans		(403)	(347)
United States
Change in benefit obligation:
Benefit obligation at beginning of year		99	107
Service cost		3	3	$ 3
Interest cost		4	4	4
Benefits paid		(7)	(5)
Actuarial loss (gain)		15	(10)
Plan amendments, settlements and curtailments		0	0
Foreign currency translation/other		(1)	0
Benefit obligation at end of year		113	99	107
Change in plan assets:
Beginning Balance		97	84
Employer contributions		0	22
Actual return on plan assets		17	(4)
Benefits paid		(7)	(5)
Plan amendments, settlements and curtailments		0	0
Foreign currency translation/other		(2)	0
Ending Balance		105	97	84
Unfunded status of the plans		(8)	(2)
International defined benefit pension plans
Change in benefit obligation:
Benefit obligation at beginning of year		763	843
Service cost		9	9	12
Interest cost		19	19	21
Benefits paid		(28)	(36)
Actuarial loss (gain)		104	(20)
Plan amendments, settlements and curtailments		(23)	3
Foreign currency translation/other		2	(55)
Benefit obligation at end of year		846	763	843
Change in plan assets:
Beginning Balance		470	544
Employer contributions		16	16
Actual return on plan assets		52	(20)
Benefits paid		(28)	(36)
Plan amendments, settlements and curtailments		(23)	0
Foreign currency translation/other		13	(34)
Ending Balance		500	470	$ 544
Unfunded status of the plans		$ (346)	$ (293)