Segment Information - Information about Company's Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Segment Reporting Information [Line Items]
Net income (loss)	$ 280,401	$ 275,344	$ 808,702	$ 788,697
Business Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)	23,995	25,038	74,160	73,763
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)	108,422	100,705	312,926	303,637
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Net income (loss)	85,312	78,676	250,501	230,254
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Net income (loss)	5,113	12,495	21,823	38,898
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)	21,150	22,749	75,462	64,680
Retail Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)	64,721	72,057	202,415	214,064
All Other [Member]
Segment Reporting Information [Line Items]
Net income (loss)	(28,312)	(36,376)	(128,585)	(136,599)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	1,132,526	1,120,170	3,412,472	3,322,236
Operating Segments [Member] | Business Banking [Member]
Segment Reporting Information [Line Items]
Total revenues	112,650	113,425	332,341	337,929
Operating Segments [Member] | Commercial Banking [Member]
Segment Reporting Information [Line Items]
Total revenues	270,554	247,282	774,392	748,978
Operating Segments [Member] | Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Total revenues	181,478	170,772	535,909	500,814
Operating Segments [Member] | Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Total revenues	13,773	24,835	49,724	79,404
Operating Segments [Member] | Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Total revenues	99,518	104,092	310,843	299,237
Operating Segments [Member] | Retail Banking [Member]
Segment Reporting Information [Line Items]
Total revenues	308,520	316,052	914,484	934,386
Operating Segments [Member] | All Other [Member]
Segment Reporting Information [Line Items]
Total revenues	146,033	143,712	494,779	421,488
Intersegment Activity Eliminated in Consolidated Totals [Member] | Business Banking [Member]
Segment Reporting Information [Line Items]
Total revenues	1,167	1,082	3,334	3,359
Intersegment Activity Eliminated in Consolidated Totals [Member] | Commercial Banking [Member]
Segment Reporting Information [Line Items]
Total revenues	1,097	1,281	3,281	3,834
Intersegment Activity Eliminated in Consolidated Totals [Member] | Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Total revenues	469	442	978	1,315
Intersegment Activity Eliminated in Consolidated Totals [Member] | Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Total revenues	(5,365)	(5,478)	(16,184)	(15,799)
Intersegment Activity Eliminated in Consolidated Totals [Member] | Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Total revenues	12,918	12,875	36,741	34,395
Intersegment Activity Eliminated in Consolidated Totals [Member] | Retail Banking [Member]
Segment Reporting Information [Line Items]
Total revenues	3,292	3,735	9,688	11,137
Intersegment Activity Eliminated in Consolidated Totals [Member] | All Other [Member]
Segment Reporting Information [Line Items]
Total revenues	$ (13,578)	$ (13,937)	$ (37,838)	$ (38,241)