Retirement Plans - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Information on postretirement medical plan		Additionally, we maintain an unfunded postretirement medical plan that provides health benefits to certain qualified retirees from ages 55 through 65.
Net asset value per fund share related to short-term investment funds		$ 1
Short-term investment funds valued - NAV		short-term investment funds that provide for daily investments and redemptions and are valued and carried at a $1 net asset value (NAV) per fund share
Budgeted contributions to funded pension plans for next year		$ 52
Expense for defined contribution plans		$ 25	$ 28	$ 32
Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Current target allocations for plan assets		50.00%
Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Current target allocations for plan assets		25.00%
Other Types of Investments
Defined Benefit Plan Disclosure [Line Items]
Current target allocations for plan assets		25.00%
Scenario Forecast
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost	$ 61
Amortization of unrecognized net actuarial losses	$ 67
Funded and Unfunded Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation		$ 2,471	2,223
Net periodic benefit cost		62	94	53
Amortization of unrecognized net actuarial losses		60	75	$ 32
Unfunded Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation		$ 203	$ 196