Retirement Plans - Fair value of pension plan assets (Details) - USD ($) $ in Millions	12 Months Ended
	Jan. 04, 2020	Dec. 29, 2018	Dec. 30, 2017
Change in fair value of plan assets
Valuation of owned properties period	3 years
Level 1
Change in fair value of plan assets
Fair value of total pension plan assets	$ 2,808	$ 2,742
Level 2
Change in fair value of plan assets
Fair value of total pension plan assets	1,382	1,217
Unobservable Inputs Level 3
Change in fair value of plan assets
Fair value of total pension plan assets	473	460
Not Subject to Leveling
Change in fair value of plan assets
Fair value of total pension plan assets	3,466	2,703
Cash and equivalents | Level 1
Change in fair value of plan assets
Fair value of total pension plan assets	18	19
Cash and equivalents | Level 2
Change in fair value of plan assets
Fair value of total pension plan assets	12	19
Cash and equivalents | Not Subject to Leveling
Change in fair value of plan assets
Fair value of total pension plan assets	174	113
Domestic Equity Securities | Level 1
Change in fair value of plan assets
Fair value of total pension plan assets	1,257	1,256
Domestic Equity Securities | Not Subject to Leveling
Change in fair value of plan assets
Fair value of total pension plan assets	1,160	828
International Equity Securities | Level 1
Change in fair value of plan assets
Fair value of total pension plan assets	929	835
International Equity Securities | Not Subject to Leveling
Change in fair value of plan assets
Fair value of total pension plan assets	780	450
Mutual Funds | Level 1
Change in fair value of plan assets
Fair value of total pension plan assets	176	266
National, state and local governments debt securities | Level 1
Change in fair value of plan assets
Fair value of total pension plan assets	414	366
National, state and local governments debt securities | Level 2
Change in fair value of plan assets
Fair value of total pension plan assets	308	290
National, state and local governments debt securities | Not Subject to Leveling
Change in fair value of plan assets
Fair value of total pension plan assets	56	53
Corporate debt securities | Level 1
Change in fair value of plan assets
Fair value of total pension plan assets	14
Corporate debt securities | Level 2
Change in fair value of plan assets
Fair value of total pension plan assets	1,062	908
Corporate debt securities | Not Subject to Leveling
Change in fair value of plan assets
Fair value of total pension plan assets	240	220
Asset-backed debt securities | Not Subject to Leveling
Change in fair value of plan assets
Fair value of total pension plan assets	18	104
Private investment partnerships | Not Subject to Leveling
Change in fair value of plan assets
Fair value of total pension plan assets	745	650
Real estate | Unobservable Inputs Level 3
Change in fair value of plan assets
Fair value of total pension plan assets	473	460	$ 460
Real estate | Not Subject to Leveling
Change in fair value of plan assets
Fair value of total pension plan assets	$ 293	$ 285