Pension, Retiree Medical and Savings Plans (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 26, 2015	Dec. 27, 2014
Defined Benefit Plan Disclosure [Line Items]
Lower limit of net accumulated gain or loss		10.00%
Average remaining service period of active plan participants, pension expense		11
Average remaining service period of active plan participants, retiree medical expense		7
Pension strategy investment term, years		5 years
Defined Contribution Plan, Cost Recognized		$ 164	$ 148	$ 130
Change in accounting estimate		125
Change in Accounting Estimate after Tax		$ 81
Change in Accounting Estimate per Share		$ 0.06
Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Unfunded plans included in total projected benefit liability		$ 790
Employer contributions		$ 659	$ 162	$ 591
Retiree Medical Plan
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets		7.50%	7.50%	7.50%
Employer contributions		$ 36	$ 43	$ 64
United States Pension Plan of US Entity, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets		7.50%	7.50%	7.50%
Employer contributions		$ 541	$ 66
Discretionary contribution to fund pension settlement		452		$ 388
Pre-tax non-cash settlement charge		242		141
Pension-related settlement, after-tax		$ 162
Pre-tax non-cash settlement charge, after-tax				$ 88
Pre-tax non-cash settlement charge, net of tax, per share		$ 0.11		$ 0.06
Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Redemption period		45
Scenario, Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Average remaining life expectancy of Inactive Plan Participants, Pension Expense	27
Expected future employer contributions in 2017	$ 184
Cost Savings Related to Reorganization of U.S. Pension Plans	40
Scenario, Forecast [Member] | Retiree Medical Plan
Defined Benefit Plan Disclosure [Line Items]
Expected future employer contributions in 2017	$ 54
Maximum | Years 1 Through 5 [Member]
Defined Benefit Plan Disclosure [Line Items]
Subsidies expected to be received under the 2003 Medicare Act		$ 3