Casualty, Environmental and Other Reserves - Narrative (Details)	1 Months Ended	2 Months Ended
	Jun. 30, 2018 USD ($)	May 31, 2018 USD ($)	Sep. 30, 2018 USD ($) claim site	Dec. 31, 2017 USD ($)
All Contingencies Reserves [Line Items]
Total reserves			$ 341,000,000	$ 374,000,000
Casualty
All Contingencies Reserves [Line Items]
Total reserves			$ 204,000,000	228,000,000
Self-insured retention amount, per occurrence	$ 75,000,000	$ 50,000,000
Number of individual claims expected to exceed self insured retention amount | claim			0
Environmental
All Contingencies Reserves [Line Items]
Total reserves			$ 89,000,000	90,000,000
Environmental impaired sites | site			216
Other
All Contingencies Reserves [Line Items]
Total reserves			$ 48,000,000	$ 56,000,000