Casualty, Environmental and Other Reserves - Casualty, Environmental and Other Reserves (Details) - USD ($) $ in Millions	Dec. 30, 2016	Dec. 25, 2015	Dec. 26, 2014	Dec. 27, 2013
Contingencies [Line Items]
Current	$ 115	$ 131
Long-term	259	269
Casualty, Environmental and Other
Contingencies [Line Items]
Current	115	131
Long-term	259	269
Total	374	400	$ 418	$ 451
Casualty Reserves
Contingencies [Line Items]
Current	53	69
Long-term	176	200
Total	229	269	265	280
Personal Injury
Contingencies [Line Items]
Current	46	57
Long-term	124	147
Total	170	204
Occupational
Contingencies [Line Items]
Current	7	12
Long-term	52	53
Total	59	65
Environmental
Contingencies [Line Items]
Current	42	42
Long-term	53	40
Total	95	82	94	100
Other Reserves
Contingencies [Line Items]
Current	20	20
Long-term	30	29
Total	$ 50	$ 49	$ 59	$ 71