Investment Securities - Gains and Losses Recognized in Income from Securities (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Available-for-sale debt and other securities:
Realized gains	$ 16	$ 46	$ 24	$ 47
Realized losses	(3)	(1)	(14)	(2)
Impairment losses	(12)	0	(19)	0
Net (losses) gains on available-for sale debt and other securities	1	45	(9)	45
Total trading debt securities (losses) gains	(1)	(1)	(1)	3
Total equity securities gains (losses)	(1)	6	20	3
Total gains (losses) recognized in income from available-for-sale debt and other securities, trading debt securities and equity securities	(1)	50	10	51
Equity securities, unrealized gains (losses)	(3)	(1)	14	(3)
Commercial Banking Revenue and Wealth and Asset Management Revenue
Investment Holdings [Line Items]
Securities gains (losses)	$ (1)	$ 1	$ (4)	$ 7