Retirement Plans - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
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
Budgeted contributions to funded pension plans for next year		$ 44
Expense for defined contribution plans		$ 22	$ 25	$ 28
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]
Service cost	$ 55
Interest cost	90
Amortization of unrecognized net actuarial losses	50
Expected return on plan assets	195
Expected decrease in service cost and interest cost	$ 12
Funded and Unfunded Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation		$ 2,679	2,471
Service cost		49	60	67
Interest cost		102	107	102
Amortization of unrecognized net actuarial losses		58	60	75
Expected return on plan assets		168	166	$ 168
Unfunded Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation		190	203
Service cost		13	16
Interest cost		$ 9	$ 9