Nature of Operations and Significant Accounting Policies - Restructuring Charges (Details) - USD ($) $ in Millions	3 Months Ended				12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2017	Dec. 30, 2016	Dec. 25, 2015
Restructuring Cost and Reserve [Line Items]
Restructuring Charge (Note 1)					$ 325	$ 0	$ 0
Cash Payments for Restructuring Charge					(187)	$ 0	$ 0
Management streamlining
Restructuring Cost and Reserve [Line Items]
Restructuring Charge (Note 1)	$ 29	$ 1	$ 122	$ 173	325
Cash Payments for Restructuring Charge					(187)
Non-cash Items					(124)
Liability	14				14
Management streamlining | Subtotal Management Workforce Reduction
Restructuring Cost and Reserve [Line Items]
Restructuring Charge (Note 1)	17	0	22	155	194
Cash Payments for Restructuring Charge					(92)
Non-cash Items					(88)
Liability	14				14
Management streamlining | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring Charge (Note 1)	7	0	10	81	98
Cash Payments for Restructuring Charge					(86)
Non-cash Items					0
Liability	12				12
Management streamlining | Pension and Other Post-Retirement Benefit Charges
Restructuring Cost and Reserve [Line Items]
Restructuring Charge (Note 1)	3	0	7	63	73
Cash Payments for Restructuring Charge					0
Non-cash Items					(73)
Liability	0				0
Management streamlining | Share-Based Compensation Remeasurement
Restructuring Cost and Reserve [Line Items]
Restructuring Charge (Note 1)	7	0	3	5	15
Cash Payments for Restructuring Charge					0
Non-cash Items					(15)
Liability	0				0
Management streamlining | Relocation
Restructuring Cost and Reserve [Line Items]
Restructuring Charge (Note 1)	0	0	2	6	8
Cash Payments for Restructuring Charge					(6)
Non-cash Items					0
Liability	2				2
Management streamlining | Reimbursement Arrangements
Restructuring Cost and Reserve [Line Items]
Restructuring Charge (Note 1)	0	0	84	0	84
Cash Payments for Restructuring Charge					(84)
Non-cash Items					0
Liability	0				0
Management streamlining | Non-Cash Executive Equity Awards Proration
Restructuring Cost and Reserve [Line Items]
Restructuring Charge (Note 1)	0	0	16	8	24
Cash Payments for Restructuring Charge					0
Non-cash Items					(24)
Liability	0				0
Management streamlining | Non-Cash Pension Settlement Charge
Restructuring Cost and Reserve [Line Items]
Restructuring Charge (Note 1)	12	0	0	0	12
Cash Payments for Restructuring Charge					0
Non-cash Items					(12)
Liability	0				0
Management streamlining | Other Charges Including Fees Related to Shareholder Matters
Restructuring Cost and Reserve [Line Items]
Restructuring Charge (Note 1)	0	$ 1	$ 0	$ 10	11
Cash Payments for Restructuring Charge					(11)
Non-cash Items					0
Liability	$ 0				$ 0