Pension and Other Postretirement Benefits - Additional Information (Detail) - USD ($)				3 Months Ended	12 Months Ended
	Apr. 01, 2018	Apr. 18, 2017	Aug. 01, 2016	Sep. 30, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Average duration refined yield curve model parallels the plans, years						11 years
Rate of compensation increase						3.50%	3.50%	3.50%
Average period of historical returns used to calculate expected future returns, in years						5 years
Decrease in expected long-term rate of return						0.75%		0.25%
Pension and other postretirement plans, expected long-term rate of return, average of actual results, period of measurement						20 years
Expected long term rate of return on plan assets						7.75%	7.75%	7.75%
Health care cost trend rate assumed for next year						5.50%	5.50%	5.50%
Number of years over actual annual health care cost trend experience						3 years
Health care cost trend rate						4.50%	4.50%	4.50%
Cash contribution to pension plans						$ 310,000,000	$ 290,000,000	$ 470,000,000
Minimum required cash contribution to pension plan				$ 50,000,000		350,000,000
Aggregate cash cash contribution to pension plan				$ 150,000,000
Cash contribution term to pension plan				30 months
Employer contributions		$ 50,000,000
Expenses related to saving and investment plans						$ 89,000,000	71,000,000	83,000,000
Maximum
Defined Benefit Plan Disclosure [Line Items]
Health care cost trend rate						9.00%
Minimum
Defined Benefit Plan Disclosure [Line Items]
Health care cost trend rate						2.20%
Scenario, Forecast
Defined Benefit Plan Disclosure [Line Items]
Expected long term rate of return on plan assets					7.00%
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Accumulated (increase) decrease in net actuarial loss after-tax, plan amendment						$ 0	0	(9,000,000)
Rate of compensation increase						3.50%
Average period over which rate of compensation increases, years						5 years
Change in interest cost component of net periodic benefit cost determination						$ 34,000,000	84,000,000
Employer contributions						310,000,000	296,000,000
Other postretirement benefits
Defined Benefit Plan Disclosure [Line Items]
Accumulated (increase) decrease in net actuarial loss after-tax, plan amendment						0	0	$ 4,000,000
Change in interest cost component of net periodic benefit cost determination						6,000,000	14,000,000
Employer contributions						0	$ 0
United Steelworkers Labor Agreement
Defined Benefit Plan Disclosure [Line Items]
Increase in pension liability, plan amendment			$ 845,000,000
Accumulated (increase) decrease in net actuarial loss after-tax, plan amendment			$ (551,000,000)
United States
Defined Benefit Plan Disclosure [Line Items]
Minimum required cash contribution to pension plan						$ 320,000,000
Subsequent Event | Salaried And Retirement Savings Plan
Defined Benefit Plan Disclosure [Line Items]
Retirement savings plan, employer contribution, percent	3.00%
Retirement savings plan, additional employer contribution, percent	3.00%