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Goodwill - Summary of Changes in the Carrying Amount of Goodwill by Segment (Parenthetical) (Detail) - USD ($)
$ in Billions
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Goodwill [Line Items]      
Accumulated goodwill impairment $ 25.6 $ 21.0 $ 21.0