Shareholders' Equity - Components of accumulated other comprehensive loss (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 30, 2017	Dec. 29, 2018	Dec. 30, 2017	Dec. 31, 2016
Components of Accumulated Other Comprehensive Loss
Beginning of period		$ (1,375)
End of period	$ (1,375)	$ (1,762)	$ (1,375)
U.S. federal statutory income tax rate (as a percent)	21.00%	21.00%	35.00%	35.00%
Accumulated Other Comprehensive Loss
Components of Accumulated Other Comprehensive Loss
Beginning of period		$ (1,375)	$ (1,605)
Other comprehensive income before reclassifications		(255)	131
Reclassified from Accumulated other comprehensive loss		125	99
Reclassification of stranded tax effects		(257)
End of period	$ (1,375)	(1,762)	(1,375)	$ (1,605)
Pension and Postretirement Benefits Adjustments
Components of Accumulated Other Comprehensive Loss
Beginning of period		(1,396)	(1,505)
Other comprehensive income before reclassifications		(198)	16
Reclassified from Accumulated other comprehensive loss		124	93
Reclassification of stranded tax effects		(257)
End of period	(1,396)	(1,727)	(1,396)	(1,505)
Foreign Currency Translation Adjustments
Components of Accumulated Other Comprehensive Loss
Beginning of period		11	(96)
Other comprehensive income before reclassifications		(49)	107
Reclassified from Accumulated other comprehensive loss		6
End of period	11	(32)	11	(96)
Deferred Gains (Losses) on Hedge Contracts
Components of Accumulated Other Comprehensive Loss
Beginning of period		10	(4)
Other comprehensive income before reclassifications		(8)	8
Reclassified from Accumulated other comprehensive loss		(5)	6
End of period	$ 10	$ (3)	$ 10	$ (4)