Parent Company Condensed Financial Statements (Condensed Statement of Income) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of income
Interest expense on long-term debt	$ 217,849	$ 414,487	$ 265,195
Compensation and employee benefits	404,071	401,700	379,622
Amortization of tax credit and other investments	70,082	98,383	96,152
Other expense	79,489	92,249	88,042
Income tax benefit	(117,968)	(169,882)	(114,995)
NET INCOME	567,797	674,035	703,701
Parent Company
Statement of income
Other income	3	425	2
Total income	511,112	190,614	160,177
Interest expense on long-term debt	3,877	6,482	6,488
Compensation and employee benefits	6,210	5,479	5,559
Amortization of tax credit and other investments	1,248	8,437	413
Other expense	1,184	1,487	1,490
Total expense	12,519	21,885	13,950
Income before income tax benefit and equity in undistributed income of subsidiaries	498,593	168,729	146,227
Income tax benefit	4,158	6,737	3,404
Undistributed earnings of subsidiaries, primarily bank	65,046	498,569	554,070
NET INCOME	567,797	674,035	703,701
Parent Company | Bank
Statement of income
Dividends from subsidiaries	511,000	190,000	160,000
Parent Company | Nonbank
Statement of income
Dividends from subsidiaries	$ 109	$ 189	$ 175