Assumptions Used to Determine Periodic Benefit Cost (Detail)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Schedule Of Defined Benefit Plans Disclosures [Line Items]
Long-term rate of return on funded assets	4.50%
Pension benefits
Schedule Of Defined Benefit Plans Disclosures [Line Items]
Discount rate	2.50%	3.10%	3.90%
Long-term rate of return on funded assets	4.50%	4.50%	4.50%
Long-term rate of compensation increase	4.00%	4.50%	4.50%
Other postretirement benefits
Schedule Of Defined Benefit Plans Disclosures [Line Items]
Discount rate	2.50%	3.10%	3.90%
Long-term rate of return on funded assets	0.00%
Long-term rate of compensation increase	4.00%	4.50%	4.50%