Retirement Plans - Amounts Recognized in Consolidated Balance Sheet (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Funded Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Noncurrent assets	$ 76	$ 22
Current liabilities	0	0
Noncurrent liabilities	0	(55)
Pension assets / (accrued benefit liability)	76	(33)
Unrecognized Net Actuarial (Gains) Losses	778	789
Postretirement Medical Plan
Defined Benefit Plan Disclosure [Line Items]
Noncurrent assets	0	0
Current liabilities	(9)	(11)
Noncurrent liabilities	(50)	(76)
Pension assets / (accrued benefit liability)	(59)	(87)
Unrecognized Net Actuarial (Gains) Losses	(32)	(10)
Unfunded Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Noncurrent assets	0	0
Current liabilities	(30)	(18)
Noncurrent liabilities	(186)	(231)
Pension assets / (accrued benefit liability)	(216)	(249)
Unrecognized Net Actuarial (Gains) Losses	$ 47	$ 84