Retirement Benefits (Reconciliation of Prior Service Credit) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Effect of curtailment		$ 1	$ (102)
Pension Plan
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Total recognized as component of net periodic benefit credit	$ (181)	(130)	(62)
Postretirement Benefits
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Total recognized as component of net periodic benefit credit	1	6	9
United States | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) | Pension Plan
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	0	0
Amortization of net loss	0	0
Ending balance, December 31	0	0	0
United States | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) | Postretirement Benefits
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	0	(3)
Amortization of net loss	0	3
Ending balance, December 31	0	0	(3)
Foreign Plan | Pension Plan
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Total recognized as component of net periodic benefit credit	(114)	(74)	(127)
Foreign Plan | Postretirement Benefits
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Total recognized as component of net periodic benefit credit	1	2	5
Foreign Plan | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) | Pension Plan
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	43	43
Amortization of net loss	(2)	(2)
Effect of curtailment	0	(1)
Total recognized as component of net periodic benefit credit	(2)	(3)
Plan amendments	(44)	0
Exchange rate adjustments	1	3
Ending balance, December 31	(2)	43	43
Foreign Plan | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) | Postretirement Benefits
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	15	0
Amortization of net loss	2	2
Effect of curtailment	0	0
Total recognized as component of net periodic benefit credit	(2)	(2)
Plan amendments	0	17
Exchange rate adjustments	(1)	0
Ending balance, December 31	$ 12	$ 15	$ 0