Investment Securities - Gains and Losses Recognized in Income from Securities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Available-for-sale debt and other securities:
Realized gains	$ 2	$ 1
Realized losses	(10)	(1)
Impairment losses	(7)	0
Net losses on available-for sale debt and other securities	(15)	0
Total trading debt securities gains	7	3
Total equity securities gains (losses)	9	(24)
Total gains recognized in income from available-for-sale debt and other securities, trading debt securities and equity securities	1	(21)
Equity securities, unrealized gains (losses)	7	(23)
Commercial Banking Revenue and Wealth and Asset Management Revenue
Investment Holdings [Line Items]
Securities gains (losses)	$ (2)	$ (2)