Off-Balance Sheet Arrangements, Guarantees and Other Commitments - Summary Information Related to Commitments to Extend Credit (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Loan commitments	$ 28,975,133	$ 21,743,359
Commercial and standby letters of credit	3,007,118	2,778,561
Total unfunded credit commitments	31,982,251	24,521,920
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for unfunded credit commitments	447,765	304,924	$ 280,903	$ 255,024
Unfunded credit commitments
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for unfunded credit commitments	$ 120,796	$ 67,656	$ 55,183	$ 51,770