Pension, Retiree Medical and Savings Plans Pension, Retiree Medical and Savings Plans (Target Asset Allocations) (Details)	Dec. 31, 2018	Dec. 30, 2017
Fixed Income
Target Asset Allocation [Line Items]
Target investment allocation percentage		40.00%
U.S. Equity
Target Asset Allocation [Line Items]
Target investment allocation percentage		33.00%
International Equity
Target Asset Allocation [Line Items]
Target investment allocation percentage		22.00%
Real Estate Funds [Member]
Target Asset Allocation [Line Items]
Target investment allocation percentage		5.00%
Scenario, Forecast [Member] | Fixed Income
Target Asset Allocation [Line Items]
Target investment allocation percentage	47.00%
Scenario, Forecast [Member] | U.S. Equity
Target Asset Allocation [Line Items]
Target investment allocation percentage	29.00%
Scenario, Forecast [Member] | International Equity
Target Asset Allocation [Line Items]
Target investment allocation percentage	20.00%
Scenario, Forecast [Member] | Real Estate Funds [Member]
Target Asset Allocation [Line Items]
Target investment allocation percentage	4.00%