Shareholders' Equity - Components of accumulated other comprehensive loss (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 29, 2018	Sep. 30, 2017
Components of Accumulated Other Comprehensive Loss
Beginning of period	$ (1,375)
End of period	(1,297)
Accumulated Other Comprehensive Loss
Components of Accumulated Other Comprehensive Loss
Beginning of period	(1,375)	$ (1,605)
Other comprehensive income before reclassifications	(26)	108
Reclassified from Accumulated other comprehensive loss	104	78
Other comprehensive income	78	186
End of period	(1,297)	(1,419)
Pension and Postretirement Benefits Adjustments
Components of Accumulated Other Comprehensive Loss
Beginning of period	(1,396)	(1,505)
Reclassified from Accumulated other comprehensive loss	100	70
Other comprehensive income	100	70
End of period	(1,296)	(1,435)
Foreign Currency Translation Adjustments
Components of Accumulated Other Comprehensive Loss
Beginning of period	11	(96)
Other comprehensive income before reclassifications	(26)	98
Reclassified from Accumulated other comprehensive loss	6
Other comprehensive income	(20)	98
End of period	(9)	2
Deferred Gains (Losses) on Hedge Contracts
Components of Accumulated Other Comprehensive Loss
Beginning of period	10	(4)
Other comprehensive income before reclassifications		10
Reclassified from Accumulated other comprehensive loss	(2)	8
Other comprehensive income	(2)	18
End of period	$ 8	$ 14