Benefit Plans - Pension Plans with Accumulated Benefit Obligation or Projected Benefit Obligation in Excess of Plan Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Pension plans with a projected benefit obligation in excess of plan assets:
Projected benefit obligation	$ 116.1	$ 120.8
Fair value of plan assets	34.4	33.7
Pension plans with an accumulated benefit obligation in excess of plan assets:
Projected benefit obligation	116.1	120.8
Fair value of plan assets	34.4	33.7
Accumulated benefit obligation	$ 112.7	$ 119.3