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Investment Securities (Gains (Losses) on Sales of Securities Available for Sale) (Details) - USD ($)
$ in Millions
6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Investment Securities Disclosure [Abstract]    
Gross Gains $ 201 $ 224
Gross Losses (166) (2)
Net Gains 35 222
Tax Expense $ 7 $ 47