Investment Securities - Gains and Losses Recognized in Income from Securities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Available-for-sale debt and other securities:
Realized gains	$ 47	$ 60	$ 72
Realized losses	(2)	(50)	(82)
OTTI	0	(1)	0
Net realized gains on available-for sale debt and other securities	45	9	(10)
Total trading debt securities gains (losses)	2	3	(15)
Total equity securities gains (losses)	17	31	(44)
Total gains (losses) recognized in income from available-for-sale debt and other securities, trading debt securities and equity securities	64	43	(69)
Equity securities, unrealized gains (losses)	7	26	$ (45)
Commercial Banking Revenue and Wealth and Asset Management Revenue
Investment Holdings [Line Items]
Securities gains (losses)	$ 5	$ 7