Loans and Allowance for Loan Losses - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Loans disclosures
Accrued interest	$ 240		$ 240
(Reversal of) provision for loan losses	49	$ 92	850	$ 217
Commercial
Loans disclosures
(Reversal of) provision for loan losses	52	50	590	102
Consumer
Loans disclosures
(Reversal of) provision for loan losses	(3)	$ 42	260	$ 120
Impact from COVID-19
Loans disclosures
Allowance for uncollectible receivables	$ 5		5
Impact from COVID-19 | Commercial
Loans disclosures
Loan Restructuring, Trial Modifications, Amount			1,900
Impact from COVID-19 | Consumer
Loans disclosures
Loan Restructuring, Trial Modifications, Amount			$ 2,400