Parent Company Financial Statements - Condensed Balance Sheet (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Investments in consolidated subsidiaries
Total assets	$ 119,872,757	$ 120,097,403
Liabilities
Long-term borrowings	6,986,186	8,444,914
Total liabilities	104,156,108	104,637,212
Shareholders’ equity	15,716,649	15,460,191	$ 16,250,819	$ 16,486,622
Total liabilities and shareholders’ equity	119,872,757	120,097,403
Parent Company [Member]
Assets
Cash in subsidiary bank	83,531	40,609
Due from consolidated bank subsidiaries
Money-market savings	876,819	856,881
Current income tax receivable	1,261	1,117
Total due from consolidated bank subsidiaries	878,080	857,998
Investments in consolidated subsidiaries
Banks	15,732,008	15,491,277
Other	301,765	324,360
Investments in trust preferred entities (note 19)	23,022	23,241
Other assets	67,732	64,187
Total assets	17,086,138	16,801,672
Liabilities
Accrued expenses and other liabilities	74,235	63,719
Long-term borrowings	1,295,254	1,277,762
Total liabilities	1,369,489	1,341,481
Shareholders’ equity	15,716,649	15,460,191
Total liabilities and shareholders’ equity	$ 17,086,138	$ 16,801,672