Casualty, Environmental and Other Reserves - Balance Sheet Presentation (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 30, 2016	Dec. 25, 2015
Contingencies [Line Items]
Current	$ 113	$ 108
Long-term	211	266
Total	324	374	$ 374	$ 400
Casualty Reserves
Contingencies [Line Items]
Current	50	49
Long-term	149	179
Total	199	228	229	269
Personal Injury
Contingencies [Line Items]
Current	40	43
Long-term	103	125
Total	143	168
Occupational
Contingencies [Line Items]
Current	10	6
Long-term	46	54
Total	56	60
Environmental
Contingencies [Line Items]
Current	39	31
Long-term	41	59
Total	80	90	95	82
Other Reserves
Contingencies [Line Items]
Current	24	28
Long-term	21	28
Total	$ 45	$ 56	$ 50	$ 49