Pension and Other Postretirement Benefits - Schedule of Obligations and Funded Status (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension benefits
Change in benefit obligation
Benefit obligation at beginning of year	$ 7,359	$ 7,026
Service cost	46	90	$ 155
Interest cost	219	234	431
Amendments	18	1
Actuarial (gains) losses	(372)	311
Settlements	(146)	0
Curtailments	(154)	0
Benefits paid	(422)	(425)
Medicare Part D subsidy receipts	0	0
Foreign currency translation impact	(72)	122
Benefit obligation at end of year	6,476	7,359	7,026
Change in plan assets
Fair value of plan assets at beginning of year	4,862	4,666
Actual return on plan assets	(144)	212
Employer contributions	298	310
Benefits paid	(397)	(404)
Administrative expenses	(33)	(33)
Settlements	(178)	0
Foreign currency translation impact	(74)	111
Fair value of plan assets at end of year	4,334	4,862	4,666
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract]
Net funded status	(2,142)	(2,497)
Amounts recognized in the Consolidated Balance Sheet consist of:
Noncurrent assets	111	89
Current liabilities	(23)	(22)
Noncurrent liabilities	(2,230)	(2,564)
Net amount recognized	(2,142)	(2,497)
Amounts recognized in Accumulated Other Comprehensive Loss consist of:
Net actuarial loss	2,957	3,240
Prior service cost (benefit)	3	10
Net amount recognized, before tax effect	2,960	3,250
Other changes in plan assets and benefit obligations recognized in Other Comprehensive Loss consist of:
Net actuarial (gain) loss	(19)	481
Amortization of accumulated net actuarial loss	(264)	(220)
Prior service cost (benefit)	19	0
Amortization of prior service (cost) benefit	(26)	(5)
Net amount recognized, before tax effect	(290)	256
Other postretirement benefits
Change in benefit obligation
Benefit obligation at beginning of year	927	980
Service cost	7	7	13
Interest cost	28	30	63
Amendments	(25)	0
Actuarial (gains) losses	(51)	1
Settlements	0	0
Curtailments	0	0
Benefits paid	(86)	(98)
Medicare Part D subsidy receipts	6	7
Foreign currency translation impact	0	0
Benefit obligation at end of year	806	927	980
Change in plan assets
Fair value of plan assets at beginning of year	0	0
Actual return on plan assets	0	0
Employer contributions	0	0
Benefits paid	0	0
Administrative expenses	0	0
Settlements	0	0
Foreign currency translation impact	0	0
Fair value of plan assets at end of year	0	0	$ 0
Defined Benefit Plan, Funded (Unfunded) Status of Plan [Abstract]
Net funded status	(806)	(927)
Amounts recognized in the Consolidated Balance Sheet consist of:
Noncurrent assets	0	0
Current liabilities	(83)	(86)
Noncurrent liabilities	(723)	(841)
Net amount recognized	(806)	(927)
Amounts recognized in Accumulated Other Comprehensive Loss consist of:
Net actuarial loss	87	146
Prior service cost (benefit)	(27)	(37)
Net amount recognized, before tax effect	60	109
Other changes in plan assets and benefit obligations recognized in Other Comprehensive Loss consist of:
Net actuarial (gain) loss	(52)	1
Amortization of accumulated net actuarial loss	(7)	(5)
Prior service cost (benefit)	(25)	0
Amortization of prior service (cost) benefit	35	8
Net amount recognized, before tax effect	(49)	4
United States | Pension benefits
Change in benefit obligation
Benefit obligation at beginning of year	6,018
Benefit obligation at end of year	5,282	6,018
Change in plan assets
Fair value of plan assets at beginning of year	3,544
Fair value of plan assets at end of year	3,123	3,544
Other changes in plan assets and benefit obligations recognized in Other Comprehensive Loss consist of:
Funded status for U.S. pension plans	$ (2,159)	$ (2,474)