Securities (Sales of Securities Available for Sale) (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Proceeds from sales	$ 16,806,062	$ 11,963,359	$ 14,847,380
Gross realized gains	3	1	13,289
Gross realized losses	(159)	(4,942)	(2,059)
Tax benefit (expense) related to securities gains/losses	$ 33	$ 1,729	$ (3,931)

The cash inflow associated with the sale of debt and equity securities classified as available-for-sale securities.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26853-111562

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (a),(b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3179-108585

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration