Commitments, Contingent Liabilities and Guarantees - Off-Balance Sheet Risks (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Financial instruments with off-balance sheet risk
Off-balance sheet risks	$ 6,637,154	$ 8,177,360
Commitments to extend credit
Financial instruments with off-balance sheet risk
Off-balance sheet risks	6,522,518	8,048,168
Standby letters of credit and guarantees on industrial revenue bonds
Financial instruments with off-balance sheet risk
Off-balance sheet risks	114,636	129,192
Commercial Loan and Lease Portfolio | Commitments to extend credit
Financial instruments with off-balance sheet risk
Off-balance sheet risks	4,396,191	5,743,072
Consumer Loan Portfolio | Commitments to extend credit
Financial instruments with off-balance sheet risk
Off-balance sheet risks	$ 2,126,327	$ 2,305,096