Shareholders' Equity - Components of accumulated other comprehensive loss (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 29, 2019	Jun. 30, 2018
Components of Accumulated Other Comprehensive Loss
Beginning of period	$ (1,762)
End of period	(1,715)
Accumulated Other Comprehensive Loss
Components of Accumulated Other Comprehensive Loss
Beginning of period	(1,762)	$ (1,375)
Other comprehensive income before reclassifications	8	(29)
Reclassified from Accumulated other comprehensive loss	39	61
End of period	(1,715)	(1,343)
Pension and Postretirement Benefits Adjustments
Components of Accumulated Other Comprehensive Loss
Beginning of period	(1,727)	(1,396)
Reclassified from Accumulated other comprehensive loss	41	62
End of period	(1,686)	(1,334)
Foreign Currency Translation Adjustments
Components of Accumulated Other Comprehensive Loss
Beginning of period	(32)	11
Other comprehensive income before reclassifications	4	(27)
End of period	(28)	(16)
Deferred Gains (Losses) on Hedge Contracts
Components of Accumulated Other Comprehensive Loss
Beginning of period	(3)	10
Other comprehensive income before reclassifications	4	(2)
Reclassified from Accumulated other comprehensive loss	(2)	(1)
End of period	$ (1)	$ 7