Investment Securities - Gains and Losses Recognized in Income from Securities (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Available-for-sale debt and other securities:
Realized gains	$ 46	$ 3	$ 47	$ 51
Realized losses	(1)	0	(2)	(47)
OTTI	0	0	0	(1)
Net realized gains on available-for sale debt and other securities	45	3	45	3
Total trading debt securities gains (losses)	(1)	0	3	5
Total equity securities gains	6	2	3	27
Total gains recognized in income from available-for-sale debt and other securities, trading debt securities and equity securities	50	5	51	35
Equity securities, unrealized gains (losses)	(1)		(3)	23
Commercial Banking Revenue and Wealth and Asset Management Revenue
Investment Holdings [Line Items]
Securities gains (losses)	$ 1	$ 2	$ 7	$ 6