Investment Securities (Gains and Losses Recognized in Income from Securities) (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Investment Holdings
Equity securities unrealized (losses) gains	$ (23)	$ 19
Commercial Banking Revenue And Wealth And Asset Management Revenue
Investment Holdings
Securities (losses) gains	$ (2)	$ 3

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