Parent Company Financial Statements - Condensed Statement of Income (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Expense
Interest on long-term borrowings	$ 189,372	$ 231,017	$ 252,766
Other expense	3,140,325	3,047,485	2,822,932
Income tax credits	(915,556)	(743,284)	(595,025)
Equity in undistributed income of subsidiaries
Net income	$ 1,408,306	$ 1,315,114	$ 1,079,667
Net income per common share
Basic	$ 8.72	$ 7.80	$ 7.22
Diluted	$ 8.70	$ 7.78	$ 7.18
Parent Company [Member]
Income
Dividends from consolidated bank subsidiaries	$ 1,540,000	$ 1,930,000	$ 480,000
Equity in earnings of Bayview Lending Group LLC	352	(10,752)	(14,267)
Other income	9,493	5,530	2,364
Total income	1,549,845	1,924,778	468,097
Expense
Interest on long-term borrowings	21,591	18,963	24,453
Other expense	19,636	21,361	16,793
Total expense	41,227	40,324	41,246
Income before income taxes and equity in undistributed income of subsidiaries	1,508,618	1,884,454	426,851
Income tax credits	26,453	17,247	19,965
Income before equity in undistributed income of subsidiaries	1,535,071	1,901,701	446,816
Equity in undistributed income of subsidiaries
Net income of subsidiaries	1,413,235	1,343,413	1,112,851
Less: dividends received	(1,540,000)	(1,930,000)	(480,000)
Equity in undistributed income of subsidiaries	(126,765)	(586,587)	632,851
Net income	$ 1,408,306	$ 1,315,114	$ 1,079,667
Net income per common share
Basic	$ 8.72	$ 7.80	$ 7.22
Diluted	$ 8.70	$ 7.78	$ 7.18