Pension Plans, Other Postretirement Benefits, and Defined-Contribution Plans - Change in Plan Assets, Funded Status of the Plans, and Amounts Recognized in the Financial Statements Table (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Change in plan assets
Employer contributions	$ 276
Pension Plans, Defined Benefit [Member]
Change in plan assets
Fair value of plan assets at beginning of year	1,340	$ 1,674
Actual return on plan assets	209	107
Employer contributions	254	101
Participant contributions	0	0
Benefit payments	(396)	(513)
Foreign-currency exchange-rate changes	17	(29)
Fair value of plan assets at end of year	1,424	1,340
Funded status of the plans at end of year	(794)	(961)
Total recognized amounts in the balance sheet consist of
Other assets	58	44
Accrued expenses	(16)	(66)
Other long-term liabilities—other	(836)	(939)
Total	(794)	(961)
Total recognized amounts in accumulated other comprehensive income consist of
Prior service (credit) cost	0	0
Net actuarial (gain) loss	501	616
Total	501	616
Other Postretirement Benefits Plan [Member]
Change in plan assets
Fair value of plan assets at beginning of year	0	0
Actual return on plan assets	0	0
Employer contributions	22	19
Participant contributions	5	4
Benefit payments	(27)	(23)
Foreign-currency exchange-rate changes	0	0
Fair value of plan assets at end of year	0	0
Funded status of the plans at end of year	(302)	(296)
Total recognized amounts in the balance sheet consist of
Other assets	0	0
Accrued expenses	(21)	(23)
Other long-term liabilities—other	(281)	(273)
Total	(302)	(296)
Total recognized amounts in accumulated other comprehensive income consist of
Prior service (credit) cost	(26)	(50)
Net actuarial (gain) loss	14	0
Total	$ (12)	$ (50)