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Pension, Retiree Medical and Savings Plans Pension, Retiree Medical and Savings Plans (Target Asset Allocations) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2016
Dec. 26, 2015
Dec. 27, 2014
Dec. 28, 2013
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 | Fixed Income        
Target Asset Allocation [Line Items]        
Target investment allocation percentage 40.00%      
Scenario, Forecast | U.S. Equity        
Target Asset Allocation [Line Items]        
Target investment allocation percentage 33.00%      
Scenario, Forecast | International Equity        
Target Asset Allocation [Line Items]        
Target investment allocation percentage 22.00%      
Scenario, Forecast | Real Estate Funds [Member]        
Target Asset Allocation [Line Items]        
Target investment allocation percentage 5.00%      
United States Pension Plan of US Entity, Defined Benefit        
Target Asset Allocation [Line Items]        
Defined Benefit Plan, Fair Value of Plan Assets   $ 11,397 $ 12,224 $ 11,462
United States Pension Plan of US Entity, Defined Benefit | Real Estate Funds [Member]        
Target Asset Allocation [Line Items]        
Defined Benefit Plan, Fair Value of Plan Assets [1],[2]   $ 735 $ 629  
[1] 2015 and 2014 amounts include $354 million and $415 million, respectively, of retiree medical plan assets that are restricted for purposes of providing health benefits for U.S. retirees and their beneficiaries.
[2] Based on the appraised value of the investments owned by these funds as determined by independent third parties using inputs that are not observable.