Employee Incentive Plans - Schedule of Stock Options Activity (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Employee Incentive Plans - Stock Options
Options Outstanding	0	0
Stock options exercised	0	0
Total intrinsic value of options exercised			$ 288

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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Number of options outstanding, including both vested and non-vested options.

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Number of share options (or share units) exercised during the current period.

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