Retirement Plans - Amounts Recognized in Consolidated Balance Sheet (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Accumulated other comprehensive (gain) loss related to retirement plans, after-tax - Deficit	$ 759	$ 601
Funded Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Noncurrent assets	45	71
Current liabilities	0	0
Noncurrent liabilities	(87)	(6)
Pension assets / (accrued benefit liability)	(42)	65
Accumulated other comprehensive loss, pre-tax	900	756
Unfunded Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Noncurrent assets	0	0
Current liabilities	(49)	(32)
Noncurrent liabilities	(220)	(210)
Pension assets / (accrued benefit liability)	(269)	(242)
Accumulated other comprehensive loss, pre-tax	86	65
Postretirement Medical Plan
Defined Benefit Plan Disclosure [Line Items]
Noncurrent assets	0	0
Current liabilities	(7)	(8)
Noncurrent liabilities	(58)	(67)
Pension assets / (accrued benefit liability)	(65)	(75)
Accumulated other comprehensive loss, pre-tax	$ (19)	$ (12)