Casualty, Environmental and Other Reserves - Schedule of Casualty, Environmental and Other Reserves (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Loss Contingencies [Line Items]
Current	$ 89	$ 90
Long-term	229	224
Total	318	314
Total Casualty
Loss Contingencies [Line Items]
Current	49	49
Long-term	151	147
Total	200	196
Personal Injury
Loss Contingencies [Line Items]
Current	38	38
Long-term	99	93
Total	137	131
Occupational
Loss Contingencies [Line Items]
Current	11	11
Long-term	52	54
Total	63	65
Environmental
Loss Contingencies [Line Items]
Current	23	23
Long-term	54	53
Total	77	76
Other
Loss Contingencies [Line Items]
Current	17	18
Long-term	24	24
Total	$ 41	$ 42