Benefit Plans - Changes in benefit obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in benefit obligation
Service cost	$ 125	$ 117	$ 119
Interest cost	254	270	269
Pension benefits
Change in benefit obligation
Benefit obligation, beginning of year	6,224	6,815
Service cost	117	110	111
Interest cost	240	255	254
Participant contributions	0	0
Actuarial (gain) loss	(927)	255
Benefits paid	(356)	(646)
Translation adjustment and other	(13)	(55)
Benefit obligation, end of year	7,139	6,224	6,815
Change in pension plan assets
Fair value of plan assets, beginning of year	5,299	6,284
Actual return on plan assets	1,235	(300)
Employer contribution	27	16
Benefits paid	(356)	(646)
Translation adjustment and other	(13)	(55)
Funded status	(947)	(925)
Fair value of plan assets, end of year	6,192	5,299	6,284
Prior service credit	(142)
Unamortized pension and other postretirement prior service credit	(142)	(198)
Postretirement benefits
Change in benefit obligation
Benefit obligation, beginning of year	375	386
Service cost	8	7	8
Interest cost	14	15	15
Participant contributions	15	13
Actuarial (gain) loss	(19)	4
Benefits paid	(39)	(35)
Translation adjustment and other	5	(7)
Benefit obligation, end of year	397	375	$ 386
Change in pension plan assets
Fair value of plan assets, beginning of year
Employer contribution	24	22
Funded status	(397)	(375)
Fair value of plan assets, end of year
Prior service credit	(13)
Unamortized pension and other postretirement prior service credit	$ (13)	$ (16)