Casualty, Environmental and Other Reserves - Schedule of Casualty, Environmental and Other Reserves (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Loss Contingencies [Line Items]
Current	$ 110	$ 108
Long-term	231	266
Total	341	374
Total Casualty
Loss Contingencies [Line Items]
Current	49	49
Long-term	155	179
Total	204	228
Personal Injury
Loss Contingencies [Line Items]
Current	42	43
Long-term	108	125
Total	150	168
Occupational
Loss Contingencies [Line Items]
Current	7	6
Long-term	47	54
Total	54	60
Environmental
Loss Contingencies [Line Items]
Current	37	31
Long-term	52	59
Total	89	90
Other
Loss Contingencies [Line Items]
Current	24	28
Long-term	24	28
Total	$ 48	$ 56