Casualty, Environmental and Other Reserves - Narrative (Details)	3 Months Ended
	Mar. 31, 2018 USD ($) claim site	Dec. 31, 2017 USD ($)
All Contingencies Reserves [Line Items]
Total reserves	$ 364,000,000	$ 374,000,000
Casualty
All Contingencies Reserves [Line Items]
Total reserves	222,000,000	228,000,000
Self-insured retention amount, per occurrence	$ 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	221
Other
All Contingencies Reserves [Line Items]
Total reserves	$ 53,000,000	$ 56,000,000