Segment Information - Information about Company's Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Net Income (Loss)	$ 473,260	$ 493,160	$ 956,002	$ 845,770
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	1,553,576	1,466,201	3,104,401	2,900,414
Business Banking [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	42,250	43,007	85,521	80,725
Business Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	140,767	136,029	280,089	263,913
Business Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	1,004	912	1,860	1,830
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	123,507	126,391	255,725	251,856
Commercial Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	278,110	269,499	545,600	535,895
Commercial Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	887	928	1,727	1,778
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	121,629	112,691	239,127	220,994
Commercial Real Estate [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	225,442	205,541	444,615	408,148
Commercial Real Estate [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	406	385	760	725
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	38,040	29,113	77,212	48,852
Discretionary Portfolio [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	60,976	58,976	124,893	109,014
Discretionary Portfolio [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	(9,291)	(10,554)	(18,590)	(21,386)
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	7,642	15,402	20,583	30,348
Residential Mortgage Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	96,449	82,167	180,210	164,625
Residential Mortgage Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	17,150	16,047	31,664	31,468
Retail Banking [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	140,494	143,089	285,560	266,469
Retail Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	436,593	420,540	867,484	814,016
Retail Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	2,787	2,707	5,298	5,572
All Other [Member]
Segment Reporting Information [Line Items]
Net Income (Loss)	(302)	23,467	(7,726)	(53,474)
All Other [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	315,239	293,449	661,510	604,803
All Other [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total Revenues	$ (12,943)	$ (10,425)	$ (22,719)	$ (19,987)