Casualty, Environmental and Other Reserves - Schedule of Casualty, Environmental and Other Reserves (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Loss Contingencies [Line Items]
Current	$ 104	$ 100
Long-term	205	205
Total	309	305
Total Casualty
Loss Contingencies [Line Items]
Current	53	48
Long-term	139	139
Total	192	187
Personal Injury
Loss Contingencies [Line Items]
Current	44	42
Long-term	85	87
Total	129	129
Occupational
Loss Contingencies [Line Items]
Current	9	6
Long-term	54	52
Total	63	58
Environmental
Loss Contingencies [Line Items]
Current	30	31
Long-term	44	43
Total	74	74
Other
Loss Contingencies [Line Items]
Current	21	21
Long-term	22	23
Total	$ 43	$ 44