Nature of Operations and Significant Accounting Policies - Retrospective Impact of Adoption of New Accounting Pronouncements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 30, 2016
Operating Expense:
Labor and Fringe	$ 2,738	$ 2,946	$ 3,135
Operating Restructuring Charge	0	240	0
Non-Operating Income (Expense):
Restructuring Charge - Non-Operating	0	(85)	0
Other Income - Net	$ 74	53	22
As Previously Reported
Operating Expense:
Labor and Fringe		2,914	3,159
Operating Restructuring Charge		325	0
Non-Operating Income (Expense):
Restructuring Charge - Non-Operating		0	0
Other Income - Net		21	46
Reclass | Accounting Standards Update 2017-07
Operating Expense:
Labor and Fringe		32	(24)
Operating Restructuring Charge		(85)	0
Non-Operating Income (Expense):
Restructuring Charge - Non-Operating		(85)	0
Other Income - Net		$ 32	$ (24)