Off-Balance Sheet Arrangements, Guarantees and Other Commitments - Summary of Commercial and Standby Letters of Credit (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Guarantor Obligations [Line Items]
Expires in One Year or Less	$ 2,949,560
Expires After One Year	108,509
Total Amount Outstanding	3,058,069	$ 2,778,561
Maximum Amount of Future Payments	3,058,069
Financial standby letters of credit
Guarantor Obligations [Line Items]
Expires in One Year or Less	2,838,280
Expires After One Year	90,452
Total Amount Outstanding	2,928,732
Maximum Amount of Future Payments	2,928,732
Performance standby letters of credit
Guarantor Obligations [Line Items]
Expires in One Year or Less	109,224
Expires After One Year	18,057
Total Amount Outstanding	127,281
Maximum Amount of Future Payments	127,281
Commercial letters of credit
Guarantor Obligations [Line Items]
Expires in One Year or Less	2,056
Expires After One Year	0
Total Amount Outstanding	2,056
Maximum Amount of Future Payments	$ 2,056