Nature of Operations and Significant Accounting Policies - Restructuring Charges (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 23, 2016	Sep. 30, 2017	Sep. 23, 2016
Restructuring Cost and Reserve [Line Items]
Restructuring Charge	$ 1			$ 0	$ 296	$ 0
Payments					(147)	$ 0
Management Streamlining Initiative
Restructuring Cost and Reserve [Line Items]
Restructuring Charge	1	$ 122	$ 173		296
Payments					(147)
Non-cash Items					(102)
Balance	47				47
Management Streamlining Initiative | Subtotal Management Workforce Reduction
Restructuring Cost and Reserve [Line Items]
Restructuring Charge	0	22	155		177
Payments					(81)
Non-cash Items					(78)
Balance	18				18
Management Streamlining Initiative | Severance
Restructuring Cost and Reserve [Line Items]
Restructuring Charge	0	10	81		91
Payments					(77)
Non-cash Items					0
Balance	14				14
Management Streamlining Initiative | Pension, Other Post-retirement Benefit and Other Non-cash Charges
Restructuring Cost and Reserve [Line Items]
Restructuring Charge	0	10	68		78
Payments					0
Non-cash Items					(78)
Balance	0				0
Management Streamlining Initiative | Relocation
Restructuring Cost and Reserve [Line Items]
Restructuring Charge	0	2	6		8
Payments					(4)
Non-cash Items					0
Balance	4				4
Management Streamlining Initiative | Reimbursement Arrangements
Restructuring Cost and Reserve [Line Items]
Restructuring Charge	0	84	0		84
Payments					(55)
Non-cash Items					0
Balance	29				29
Management Streamlining Initiative | Non-cash Executive Equity Awards Proration
Restructuring Cost and Reserve [Line Items]
Restructuring Charge	0	16	8		24
Payments					0
Non-cash Items					(24)
Balance	0				0
Management Streamlining Initiative | Other Charges Including Fees Related to Shareholder Matters
Restructuring Cost and Reserve [Line Items]
Restructuring Charge	1	$ 0	$ 10		11
Payments					(11)
Non-cash Items					0
Balance	$ 0				$ 0