Employee Postretirement Benefits (Summarized Financial Information about Postretirement plans, Excluding Defined Contribution Retirement Plans) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Pension Plans
Benefit obligation at beginning of year		$ 4,047	$ 3,687
Service cost		22	21	$ 36
Interest cost		95	121	128
Actuarial (gain) loss(a)	[1]	333	446
Currency and other		134	51
Benefit payments from plans		(169)	(142)
Direct benefit payments		(8)	(10)
Settlements and curtailments		(113)	(127)
Benefit obligation at end of year		4,341	4,047	3,687
Fair value of plan assets at beginning of year		3,803	3,398
Actual return on plan assets		489	572
Employer contributions		40	50
Currency and other		120	51
Benefit payments		(169)	(142)
Settlements		(90)	(126)
Fair value of plan assets at end of year		4,193	3,803	3,398
Funded Status		(148)	(244)
Other Postretirement Benefit Plans
Benefit obligation at beginning of year		693	673
Service cost		8	8	11
Interest cost		23	28	28
Actuarial (gain) loss(a)	[1]	42	36
Currency and other		(10)	0
Benefit payments from plans		0	0
Direct benefit payments		(47)	(52)
Settlements and curtailments		0	0
Benefit obligation at end of year		709	693	673
Fair value of plan assets at beginning of year		0	0
Actual return on plan assets		0	0
Employer contributions		0	0
Currency and other		0	0
Benefit payments		0	0
Settlements		0	0
Fair value of plan assets at end of year		0	0	$ 0
Funded Status		$ (709)	$ (693)

[1] The actuarial net losses in 2020 and 2019 were primarily due to discount rate decreases in 2020 and 2019.