Loans and Allowance for Loan Losses - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Loans disclosures
(Reversal of) provision for loan losses	$ (167)	$ 353	$ (358)	$ 801
Commercial
Loans disclosures
(Reversal of) provision for loan losses	(137)	264	(280)	538
Consumer
Loans disclosures
(Reversal of) provision for loan losses	(30)	$ 89	(78)	$ 263
Impact from COVID-19
Loans disclosures
Allowance for uncollectible receivables	$ 233		233
Impact from COVID-19 | Commercial
Loans disclosures
Loan Restructuring, Trial Modifications, Amount			58
Impact from COVID-19 | Consumer
Loans disclosures
Loan Restructuring, Trial Modifications, Amount			$ 520