Casualty, Environmental and Other Reserves - Schedule of Casualty, Environmental and Other Reserves (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Loss Contingencies [Line Items]
Current	$ 117	$ 90
Long-term	252	224
Total	369	314
Total Casualty
Loss Contingencies [Line Items]
Current	51	49
Long-term	139	147
Total	190	196
Personal Injury
Loss Contingencies [Line Items]
Current	44	38
Long-term	82	93
Total	126	131
Occupational
Loss Contingencies [Line Items]
Current	7	11
Long-term	57	54
Total	64	65
Environmental
Loss Contingencies [Line Items]
Current	36	23
Long-term	72	53
Total	108	76
Other
Loss Contingencies [Line Items]
Current	30	18
Long-term	41	24
Total	$ 71	$ 42