Investment Securities - Gains and Losses Recognized in Income from Securities (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Available-for-sale debt and other securities:
Realized gains	$ 7		$ 0	$ 8	$ 1
Realized losses	0		0	(10)	(1)
Impairment losses	0	$ (7)	0	(7)	0
Net (losses) gains on available-for sale debt and other securities	7		0	(9)	0
Total trading debt securities (losses) gains	(7)		0	0	3
Total equity securities gains (losses)	11		21	21	(3)
Total gains recognized in income from available-for-sale debt and other securities, trading debt securities and equity securities	11		21	12	0
Equity securities, unrealized gains (losses)	10		21	17	(2)
Commercial Banking Revenue and Wealth and Asset Management Revenue
Investment Holdings [Line Items]
Securities gains (losses)	$ (1)		$ 8	$ (3)	$ 6