Off-Balance Sheet Arrangements, Guarantees and Other Commitments - Summary Information Related to Commitments to Extend Credit (Excluding Letters of Credit) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Disclosure Off Balance Sheet Arrangements Guarantees And Other Commitments Additional Information [Abstract]
Loan commitments available for funding	$ 33,174		$ 28,975
Commercial and standby letters of credit	3,211		3,007
Total unfunded credit commitments	36,385		31,982
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for credit losses: loans	396	$ 392	448	$ 590	$ 549	$ 305
Unfunded Credit Commitments
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for credit losses: loans	$ 120	$ 105	$ 121	$ 99	$ 85	$ 67