Postretirement Plans - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 25, 2017	Jun. 26, 2016	Jun. 25, 2017	Jun. 26, 2016
Defined Benefit Plan Disclosure [Line Items]
Recognition of previously deferred postretirement benefit plan amounts, net of tax	$ 200,000,000	$ 173,000,000	$ 402,000,000	$ 346,000,000
Recognition of previously deferred postretirement benefit plan amounts, before tax	309,000,000	267,000,000	621,000,000	535,000,000
Other postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Recognition of previously deferred postretirement benefit plan amounts, before tax	13,000,000	5,000,000	27,000,000	10,000,000
Qualified defined benefit pension plans
Defined Benefit Plan Disclosure [Line Items]
Contributions made by the employer	$ 0	$ 0	$ 0	$ 0