Pensions and Other Postretirement Benefits-Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)
Defined Benefit Plan, Assumed Health Care Cost Trend Rates [Abstract]
Health care cost trend rate assumed for current fiscal year, participants under 65	6.50%
Health care cost trend rate assumed for current fiscal year, participants over 65	6.80%
Ultimate health care cost trend rate	4.50%
Year that rate reaches ultimate trend rate	2029
Postretirement Plans Other Than Pensions [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Expected benefit payments, in next fiscal year	$ 4
Funded status of plan, asset (liablity)	$ 45