Pension and Other Postretirement Benefits - Change in Plan Assets and Reconciliation of Funded Status (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
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	2,487	2,441
Actual return on plan assets	227	274
Company contributions	178	70
Plan participants’ contributions	2	2
Benefits paid	(152)	(150)
Foreign currency translation	90	(150)
Fair value of plan assets at December 31	2,832	2,487
Funded status
Funded status	171	(75)
Other immaterial plans	(65)	(58)
Net asset (liability) at end of year	106	(133)
The amounts recognized in the statement of financial position as of December 31 consist of:
Net asset (liability) at end of year	106	(133)
The pre-tax amounts recognized in accumulated other comprehensive income consist of:
Net actuarial (gain) loss	548	673
Prior service cost	0	0
Pre-tax net actuarial (gain) loss and prior service cost	548	673
Accumulated benefit obligation	2,499	2,207
Plans with accumulated benefit obligation in excess of plan assets as of December 31:
Projected benefit obligation	184	183
Accumulated benefit obligation	175	167
Fair value of plan assets	27	25
Other Postretirement Benefits
Change in plan assets:
Fair value of plan assets at January 1	351	342
Actual return on plan assets	45	36
Company contributions	6	4
Plan participants’ contributions	12	12
Benefits paid	(41)	(43)
Foreign currency translation	0	0
Fair value of plan assets at December 31	373	351
Funded status
Funded status	(173)	(200)
Other immaterial plans	(5)	(5)
Net asset (liability) at end of year	(178)	(205)
The amounts recognized in the statement of financial position as of December 31 consist of:
Net asset (liability) at end of year	(178)	(205)
The pre-tax amounts recognized in accumulated other comprehensive income consist of:
Net actuarial (gain) loss	(64)	(38)
Prior service cost	0	0
Pre-tax net actuarial (gain) loss and prior service cost	(64)	(38)
Other assets | Pension
The amounts recognized in the statement of financial position as of December 31 consist of:
Other assets	337	131
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	(219)	(252)
Other noncurrent liabilities | Other Postretirement Benefits
The amounts recognized in the statement of financial position as of December 31 consist of:
Other noncurrent liabilities	$ (174)	$ (201)