Retirement Plans - Fair value of pension plan assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Jan. 02, 2016	Jan. 03, 2015
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	$ 2,711	$ 2,752
Level 2
Change in fair value of plan assets
Fair value of total pension plan assets	1,068	1,169
Unobservable Inputs Level 3
Change in fair value of plan assets
Fair value of total pension plan assets	494	436
Not Subject to Leveling
Change in fair value of plan assets
Fair value of total pension plan assets	2,601	2,311
Cash and equivalents | Level 1
Change in fair value of plan assets
Fair value of total pension plan assets	26	27
Cash and equivalents | Level 2
Change in fair value of plan assets
Fair value of total pension plan assets	8	11
Cash and equivalents | Not Subject to Leveling
Change in fair value of plan assets
Fair value of total pension plan assets	156	173
Domestic Equity Securities | Level 1
Change in fair value of plan assets
Fair value of total pension plan assets	1,262	1,252
Domestic Equity Securities | Not Subject to Leveling
Change in fair value of plan assets
Fair value of total pension plan assets	618	595
International Equity Securities | Level 1
Change in fair value of plan assets
Fair value of total pension plan assets	773	812
International Equity Securities | Not Subject to Leveling
Change in fair value of plan assets
Fair value of total pension plan assets	510	360
Mutual Funds | Level 1
Change in fair value of plan assets
Fair value of total pension plan assets	309	251
National, state and local governments debt securities | Level 1
Change in fair value of plan assets
Fair value of total pension plan assets	341	410
National, state and local governments debt securities | Level 2
Change in fair value of plan assets
Fair value of total pension plan assets	246	314
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	44	43
Corporate debt securities | Level 2
Change in fair value of plan assets
Fair value of total pension plan assets	769	752
Corporate debt securities | Not Subject to Leveling
Change in fair value of plan assets
Fair value of total pension plan assets	121	126
Asset-backed debt securities | Level 2
Change in fair value of plan assets
Fair value of total pension plan assets	45	92
Asset-backed debt securities | Not Subject to Leveling
Change in fair value of plan assets
Fair value of total pension plan assets	100
Real estate | Unobservable Inputs Level 3
Change in fair value of plan assets
Fair value of total pension plan assets	494	436	$ 436
Real estate | Not Subject to Leveling
Change in fair value of plan assets
Fair value of total pension plan assets	292	322
Private investment partnerships | Not Subject to Leveling
Change in fair value of plan assets
Fair value of total pension plan assets	506	441
Hedge funds | Not Subject to Leveling
Change in fair value of plan assets
Fair value of total pension plan assets	$ 254	$ 251