Casualty, Environmental and Other Reserves - Casualty, Environmental and Other Reserves (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 30, 2016	Dec. 25, 2015	Dec. 26, 2014
Contingencies [Line Items]
Current	$ 108	$ 115
Long-term	266	259
Total	374	374	$ 400	$ 418
Casualty Reserves
Contingencies [Line Items]
Current	49	53
Long-term	179	176
Total	228	229	269	265
Personal Injury
Contingencies [Line Items]
Current	43	46
Long-term	125	124
Total	168	170
Occupational
Contingencies [Line Items]
Current	6	7
Long-term	54	52
Total	60	59
Environmental
Contingencies [Line Items]
Current	31	42
Long-term	59	53
Total	90	95	82	94
Other Reserves
Contingencies [Line Items]
Current	28	20
Long-term	28	30
Total	$ 56	$ 50	$ 49	$ 59