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Pension Plans and Other Postretirement Benefits - Fair Values of Company's Pension Plan Assets by Asset Category (Parenthetical) (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]    
Interest and dividend receivable on plan assets $ 2 $ 2
High-Yielding Bonds [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Investment in mutual funds 20.00% 23.00%
Investment Grade Bonds [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Investment in mutual funds 80.00% 77.00%