Casualty, Environmental and Other Reserves - Schedule of Casualty, Environmental and Other Reserves (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Loss Contingencies [Line Items]
Current	$ 110	$ 113
Long-term	199	211
Total	309	324
Total Casualty
Loss Contingencies [Line Items]
Current	56	50
Long-term	132	149
Total	188	199
Personal Injury
Loss Contingencies [Line Items]
Current	47	40
Long-term	83	103
Total	130	143
Occupational
Loss Contingencies [Line Items]
Current	9	10
Long-term	49	46
Total	58	56
Environmental
Loss Contingencies [Line Items]
Current	32	39
Long-term	46	41
Total	78	80
Other
Loss Contingencies [Line Items]
Current	22	24
Long-term	21	21
Total	$ 43	$ 45