Shareholders' Equity - Components of accumulated other comprehensive loss (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jul. 01, 2017
Components of Accumulated Other Comprehensive Loss
Beginning of period	$ (1,375)	$ (1,605)
Other comprehensive income before reclassifications	(29)	67
Reclassified from Accumulated other comprehensive loss	61	52
Other comprehensive income	32	119
End of period	(1,343)	(1,486)
Pension and Postretirement Benefits Adjustments
Components of Accumulated Other Comprehensive Loss
Beginning of period	(1,396)	(1,505)
Reclassified from Accumulated other comprehensive loss	62	47
Other comprehensive income	62	47
End of period	(1,334)	(1,458)
Foreign Currency Translation Adjustments
Components of Accumulated Other Comprehensive Loss
Beginning of period	11	(96)
Other comprehensive income before reclassifications	(27)	64
Other comprehensive income	(27)	64
End of period	(16)	(32)
Deferred Gains (Losses) on Hedge Contracts
Components of Accumulated Other Comprehensive Loss
Beginning of period	10	(4)
Other comprehensive income before reclassifications	(2)	3
Reclassified from Accumulated other comprehensive loss	(1)	5
Other comprehensive income	(3)	8
End of period	$ 7	$ 4