Pension, Retiree Medical and Savings Plans (Estimated Future Benefit Payments) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 21, 2020	Dec. 28, 2019	Dec. 29, 2018	Dec. 30, 2017
Member-Plan A [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions/funding		$ 400	$ 1,400
Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions/funding		550	1,495
Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Discretionary		417	1,417	$ 6
Non-discretionary		255	198	158
2020		945
2021		915
2022		900
2023		930
2024		970
2025-29		5,275
Employer contributions/funding		672	1,615	164
Retiree Medical Plan
Defined Benefit Plan Disclosure [Line Items]
Discretionary		0	37	0
Non-discretionary		44	56	56
2020		100
2021		95
2022		95
2023		90
2024		85
2025-29		355
Employer contributions/funding		44	$ 93	$ 56
Years 2025 Through 2029
Defined Benefit Plan Disclosure [Line Items]
Subsidies expected to be received under the 2003 Medicare Act		4
Maximum | Years 2020 Through 2024
Defined Benefit Plan Disclosure [Line Items]
Subsidies expected to be received under the 2003 Medicare Act		$ 2
Forecast [Member] | Pension Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Discretionary	$ 150
Non-discretionary	150
Forecast [Member] | Retiree Medical Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Non-discretionary	$ 60