Casualty, Environmental and Other Reserves - Schedule of Casualty, Environmental and Other Reserves (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Loss Contingencies [Line Items]
Current	$ 106	$ 108
Long-term	258	266
Total	364	374
Total Casualty
Loss Contingencies [Line Items]
Current	49	49
Long-term	173	179
Total	222	228
Personal Injury
Loss Contingencies [Line Items]
Current	42	43
Long-term	120	125
Total	162	168
Occupational
Loss Contingencies [Line Items]
Current	7	6
Long-term	53	54
Total	60	60
Environmental
Loss Contingencies [Line Items]
Current	31	31
Long-term	58	59
Total	89	90
Other
Loss Contingencies [Line Items]
Current	26	28
Long-term	27	28
Total	$ 53	$ 56