Employee Benefit Plans and Other Postretirement Benefits - Fair Value Measurements of Plan Assets (Parenthetical) (Details) - Private Equity Securities - Significant unobservable input (Level 3) $ in Millions	Dec. 31, 2020 USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investment commitment	$ 15.0
Unfunded portion of investment commitment	$ 2.0