Pension and Other Postretirement Benefits - Change in Plan Assets and Reconciliation of Funded Status (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
The amounts recognized in the statement of financial position as of December 31 consist of:
Accrued expenses	$ (16)	$ (16)
Pension
Change in plan assets:
Fair value of plan assets at January 1	2,832	2,487
Actual return on plan assets	(82)	227
Company contributions	23	178
Plan participants’ contributions	2	2
Benefits paid	(165)	(152)
Foreign currency translation	(60)	90
Fair value of plan assets at December 31	2,550	2,832
Funded status
Funded status	121	171
Other immaterial plans	(46)	(65)
Net asset (liability) at end of year	75	106
The amounts recognized in the statement of financial position as of December 31 consist of:
Net asset (liability) at end of year	75	106
The pre-tax amounts recognized in accumulated other comprehensive income consist of:
Net actuarial (gain) loss	552	548
Prior service cost	8	0
Pre-tax net actuarial (gain) loss and prior service cost	560	548
Accumulated benefit obligation	2,299	2,499
Plans with accumulated benefit obligation in excess of plan assets as of December 31:
Projected benefit obligation	176	184
Accumulated benefit obligation	170	175
Fair value of plan assets	28	27
Other Postretirement Benefits
Change in plan assets:
Fair value of plan assets at January 1	373	351
Actual return on plan assets	(19)	45
Company contributions	7	6
Plan participants’ contributions	12	12
Benefits paid	(40)	(41)
Foreign currency translation	0	0
Fair value of plan assets at December 31	333	373
Funded status
Funded status	(178)	(173)
Other immaterial plans	(5)	(5)
Net asset (liability) at end of year	(183)	(178)
The amounts recognized in the statement of financial position as of December 31 consist of:
Net asset (liability) at end of year	(183)	(178)
The pre-tax amounts recognized in accumulated other comprehensive income consist of:
Net actuarial (gain) loss	(53)	(64)
Prior service cost	0	0
Pre-tax net actuarial (gain) loss and prior service cost	(53)	(64)
Other assets | Pension
The amounts recognized in the statement of financial position as of December 31 consist of:
Other assets	290	337
Other assets | Other Postretirement Benefits
The amounts recognized in the statement of financial position as of December 31 consist of:
Other assets	0	0
Accrued expenses | Pension
The amounts recognized in the statement of financial position as of December 31 consist of:
Accrued expenses	(12)	(12)
Accrued expenses | Other Postretirement Benefits
The amounts recognized in the statement of financial position as of December 31 consist of:
Accrued expenses	(4)	(4)
Other noncurrent liabilities | Pension
The amounts recognized in the statement of financial position as of December 31 consist of:
Other noncurrent liabilities	(203)	(219)
Other noncurrent liabilities | Other Postretirement Benefits
The amounts recognized in the statement of financial position as of December 31 consist of:
Other noncurrent liabilities	$ (179)	$ (174)