Parent Company Financial Statements - Condensed Balance Sheet (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Investments in consolidated subsidiaries
Total assets	$ 120,097,403	$ 118,593,487
Liabilities
Long-term borrowings	8,444,914	8,141,430
Total liabilities	104,637,212	102,342,668
Shareholders’ equity	15,460,191	16,250,819	$ 16,486,622	$ 16,173,289
Total liabilities and shareholders’ equity	120,097,403	118,593,487
Parent Company [Member]
Assets
Cash in subsidiary bank	40,609	13,379
Due from consolidated bank subsidiaries
Money-market savings	856,881	1,616,147
Current income tax receivable	1,117	4,437
Total due from consolidated bank subsidiaries	857,998	1,620,584
Investments in consolidated subsidiaries
Banks	15,491,277	14,841,794
Other	324,360	253,904
Investments in trust preferred entities (note 19)	23,241	23,453
Other assets	64,187	66,023
Total assets	16,801,672	16,819,137
Liabilities
Accrued expenses and other liabilities	63,719	49,093
Long-term borrowings	1,277,762	519,225
Total liabilities	1,341,481	568,318
Shareholders’ equity	15,460,191	16,250,819
Total liabilities and shareholders’ equity	$ 16,801,672	$ 16,819,137