Casualty, Environmental and Other Reserves - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) claim site	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Loss Contingencies [Line Items]
Reserves	$ 314	$ 305	$ 324	$ 374
Casualty Reserves
Loss Contingencies [Line Items]
Reserves	$ 196	187	199	228
Individual claims expected to exceed self-insured retention amount | claim	0
Casualty Reserves | Maximum
Loss Contingencies [Line Items]
Self-insured retention amount per injury	$ 75
Personal Injury
Loss Contingencies [Line Items]
Reserves	131	129
Environmental
Loss Contingencies [Line Items]
Reserves	$ 76	74	80	90
Environmental impaired sites | site	220
Other
Loss Contingencies [Line Items]
Reserves	$ 42	$ 44	$ 45	$ 56