Commitments and Contingencies Environmental (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) sites	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) sites	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Environmental Issue [Member]
Loss Contingencies [Line Items]
Number of alleged environmental contamination sites (in sites) | sites	206		206
Number of environmental superfund sites (in sites) | sites	18		18
Recorded Liability For Third Party Environmental Tort Claims	$ 8		$ 8		$ 9
Accrued obligations for environmental matters, current liabilities	$ 35		$ 35		$ 40
Years in which accrued environmental costs will be paid over	10		10
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning balance	$ 310	$ 326	$ 317	$ 342
Accruals / changes in estimates	(7)	3	(5)	2
Payments	(4)	(7)	(13)	(22)
Ending balance	299	322	299	$ 322
Environmental Issue [Member] | Minimum [Member]
Loss Contingencies [Line Items]
Future costs to settle claims and associated liability	245		245
Environmental Issue [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Future costs to settle claims and associated liability	395		$ 395
Environmental Issue [Member]
Loss Contingencies [Line Items]
Accrual for Environmental Loss Contingencies, Revision in Estimates	$ 8	$ 2