Retirement Benefits (Reconciliation of Net Actuarial Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Plan
Reconciliation of unrecognized net actuarial gain loss [Roll Forward]
Total recognized as component of net periodic benefit credit	$ (181)	$ (130)	$ (62)
Postretirement Benefits
Reconciliation of unrecognized net actuarial gain loss [Roll Forward]
Total recognized as component of net periodic benefit credit	1	6	9
United States | Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent | Pension Plan
Reconciliation of unrecognized net actuarial gain loss [Roll Forward]
Beginning balance	(1,766)	(1,720)
Amortization of net loss	55	37
Other	0	0
Liability experience	502	(538)
Asset experience	(687)	455
Total amount recognized as change in plan assets and benefit obligations	(185)	(83)
Ending balance, December 31	(1,896)	(1,766)	(1,720)
United States | Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent | Postretirement Benefits
Reconciliation of unrecognized net actuarial gain loss [Roll Forward]
Beginning balance	6	11
Amortization of net loss	(1)	(1)
Other	0	(1)
Liability experience	1	(3)
Asset experience	0	0
Total amount recognized as change in plan assets and benefit obligations	1	(4)
Ending balance, December 31	6	6	11
Foreign Plan | Pension Plan
Reconciliation of unrecognized net actuarial gain loss [Roll Forward]
Total recognized as component of net periodic benefit credit	(114)	(74)	(127)
Other	0	(13)
Foreign Plan | Postretirement Benefits
Reconciliation of unrecognized net actuarial gain loss [Roll Forward]
Total recognized as component of net periodic benefit credit	1	2	5
Other	0	0
Foreign Plan | Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent | Pension Plan
Reconciliation of unrecognized net actuarial gain loss [Roll Forward]
Beginning balance	(2,646)	(3,081)
Amortization of net loss	91	130
Effect of settlement	42	54
Total recognized as component of net periodic benefit credit	133	184
Liability experience	450	149
Asset experience	(648)	311
Plan amendments	3	(5)
Effect of curtailment	0	1
Total amount recognized as change in plan assets and benefit obligations	(195)	456
Exchange rate adjustments	140	(205)
Ending balance, December 31	(2,568)	(2,646)	(3,081)
Foreign Plan | Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent | Postretirement Benefits
Reconciliation of unrecognized net actuarial gain loss [Roll Forward]
Beginning balance	(10)	(11)
Amortization of net loss	0	1
Effect of settlement	0	0
Total recognized as component of net periodic benefit credit	0	1
Liability experience	8	0
Asset experience	0	0
Plan amendments	0	0
Effect of curtailment	0	0
Total amount recognized as change in plan assets and benefit obligations	8	0
Exchange rate adjustments	1	0
Ending balance, December 31	$ (1)	$ (10)	$ (11)