Environmental (Details) $ in Millions	3 Months Ended			12 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2017 USD ($) sites	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Environmental Issue [Member]
Loss Contingencies [Line Items]
Increase in environmental expense	$ 2	$ 8	$ 7
Environmental Issue [Member]
Loss Contingencies [Line Items]
Number of alleged environmental contamination sites (in sites) | sites				218
Number of environmental superfund sites (in sites) | sites				18
Liability for third-party tort claims				$ 9	$ 12
Accrued obligations for environmental matters, current liabilities				$ 40	40
Estimated time frame for accrued cost distributions				10
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning balance				$ 342	369	$ 404
Accruals / changes in estimates				5	5	4
Payments				(30)	(32)	(39)
Ending balance				317	$ 342	$ 369
Environmental Issue [Member] | Minimum [Member]
Loss Contingencies [Line Items]
Future costs to settle claims and associated liability				260
Environmental Issue [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Future costs to settle claims and associated liability				$ 415