Outstanding Commitments to Extend Credit and Letters of Credit (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Commercial and industrial
Valuation allowances and reserves, balance	$ 5,245,041	$ 3,997,401
Commerical mortgage and construction
Valuation allowances and reserves, balance	1,787,963	1,168,624
Real estate - home equity
Valuation allowances and reserves, balance	1,618,051	1,523,494
Total commitments to extend credit
Valuation allowances and reserves, balance	8,651,055	6,689,519
Standby letters of credit
Valuation allowances and reserves, balance	298,750	303,020
Commercial letters of credit
Valuation allowances and reserves, balance	56,229	50,432
Letter of Credit [Member]
Valuation allowances and reserves, balance	$ 354,979	$ 353,452