Parent Company Financial Statements - Condensed Balance Sheet (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Investments in consolidated subsidiaries
Total assets	$ 142,601,105	$ 119,872,757
Liabilities
Long-term borrowings	4,382,193	6,986,186
Total liabilities	126,413,822	104,156,108
Shareholders’ equity	16,187,283	15,716,649	$ 15,460,191	$ 16,250,819
Total liabilities and shareholders’ equity	142,601,105	119,872,757
Parent Company [Member]
Assets
Cash in subsidiary bank	100,593	83,531
Due from consolidated bank subsidiaries
Money-market savings	699,476	876,819
Current income tax receivable		1,261
Total due from consolidated bank subsidiaries	699,476	878,080
Investments in consolidated subsidiaries
Banks	16,554,287	15,732,008
Other	125,988	301,765
Investments in trust preferred entities (note 19)	22,846	23,022
Other assets	92,170	67,732
Total assets	17,595,360	17,086,138
Liabilities
Accrued expenses and other liabilities	96,664	74,235
Long-term borrowings	1,311,413	1,295,254
Total liabilities	1,408,077	1,369,489
Shareholders’ equity	16,187,283	15,716,649
Total liabilities and shareholders’ equity	$ 17,595,360	$ 17,086,138