XML 103 R83.htm IDEA: XBRL DOCUMENT v3.22.0.1
Pension and other post-retirement benefits - Weighted Average Assumptions Used to Determine Net Benefit Cost (Detail)
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Pension benefits    
Defined Benefit Plan Disclosure [Line Items]    
Discount rate 2.49% 3.19%
Expected return on assets 6.20% 6.85%
Rate of compensation increase 3.99% 3.96%
OPEB    
Defined Benefit Plan Disclosure [Line Items]    
Discount rate 2.58% 3.29%
Expected return on assets 4.79% 5.57%
Health care cost trend rate    
Before Age 65 5.122% 6.125%
Age 65 and after 5.122% 6.125%
Assumed ultimate medical inflation rate 4.05% 4.75%
Year in which ultimate rate is reached 2031 2031