Segment Information - Information about Company's Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Segment Reporting Information [Line Items]
Net income (loss)	$ 336,031	$ 286,688	$ 634,559	$ 528,301
Business Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)	22,747	25,354	48,195	50,165
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)	105,392	108,081	206,719	204,504
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Net income (loss)	84,088	82,598	164,617	165,189
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Net income (loss)	46,225	10,756	100,749	16,710
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)	19,980	24,852	37,057	54,312
Retail Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)	71,497	68,806	134,785	137,694
All Other [Member]
Segment Reporting Information [Line Items]
Net income (loss)	(13,898)	(33,759)	(57,563)	(100,273)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	1,312,073	1,180,155	2,604,970	2,279,946
Operating Segments [Member] | Business Banking [Member]
Segment Reporting Information [Line Items]
Total revenues	114,360	111,131	228,049	219,691
Operating Segments [Member] | Commercial Banking [Member]
Segment Reporting Information [Line Items]
Total revenues	265,481	257,257	519,098	503,838
Operating Segments [Member] | Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Total revenues	192,175	185,410	369,555	354,431
Operating Segments [Member] | Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Total revenues	98,460	20,477	209,804	35,951
Operating Segments [Member] | Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Total revenues	103,882	105,568	200,817	211,325
Operating Segments [Member] | Retail Banking [Member]
Segment Reporting Information [Line Items]
Total revenues	345,665	305,573	684,711	605,964
Operating Segments [Member] | All Other [Member]
Segment Reporting Information [Line Items]
Total revenues	192,050	194,739	392,936	348,746
Intersegment Activity Eliminated in Consolidated Totals [Member] | Business Banking [Member]
Segment Reporting Information [Line Items]
Total revenues	1,197	1,122	2,188	2,167
Intersegment Activity Eliminated in Consolidated Totals [Member] | Commercial Banking [Member]
Segment Reporting Information [Line Items]
Total revenues	911	1,099	1,967	2,184
Intersegment Activity Eliminated in Consolidated Totals [Member] | Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Total revenues	449	427	836	509
Intersegment Activity Eliminated in Consolidated Totals [Member] | Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Total revenues	(14,608)	(5,376)	(28,931)	(10,819)
Intersegment Activity Eliminated in Consolidated Totals [Member] | Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Total revenues	21,244	12,436	40,904	23,823
Intersegment Activity Eliminated in Consolidated Totals [Member] | Retail Banking [Member]
Segment Reporting Information [Line Items]
Total revenues	3,132	3,259	6,146	6,396
Intersegment Activity Eliminated in Consolidated Totals [Member] | All Other [Member]
Segment Reporting Information [Line Items]
Total revenues	$ (12,325)	$ (12,967)	$ (23,110)	$ (24,260)