Pension, Retiree Medical and Savings Plans Pension, Retiree Medical and Savings Plans (Target Asset Allocations) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016		Dec. 26, 2015	Dec. 27, 2014
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		40.00%
Scenario, Forecast [Member] | U.S. Equity
Target Asset Allocation [Line Items]
Target investment allocation percentage		33.00%
Scenario, Forecast [Member] | International Equity
Target Asset Allocation [Line Items]
Target investment allocation percentage		22.00%
Scenario, Forecast [Member] | 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			$ 11,458		$ 11,397	$ 12,224
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	[2]		$ 651	[1]	$ 735

[1] 2016 and 2015 amounts include $320 million and $354 million, respectively, of retiree medical plan assets that are restricted for purposes of providing health benefits for U.S. retirees and their beneficiaries.

[2] The real estate commingled funds include investments in limited partnerships. These funds are based on the net asset value of the appraised value of investments owned by these funds as determined by independent third parties using inputs that are not observable. The majority of the funds are redeemable quarterly subject to availability of cash and have notice periods ranging from 45 to 90 days.