Casualty, Environmental and Other Reserves - Schedule of Casualty, Environmental and Other Reserves (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Loss Contingencies [Line Items]
Current	$ 102	$ 90
Long-term	210	224
Total	312	314
Total Casualty
Loss Contingencies [Line Items]
Current	51	49
Long-term	140	147
Total	191	196
Personal Injury
Loss Contingencies [Line Items]
Current	44	38
Long-term	85	93
Total	129	131
Occupational
Loss Contingencies [Line Items]
Current	7	11
Long-term	55	54
Total	62	65
Environmental
Loss Contingencies [Line Items]
Current	30	23
Long-term	47	53
Total	77	76
Other
Loss Contingencies [Line Items]
Current	21	18
Long-term	23	24
Total	$ 44	$ 42