Segment Information - Information about Company's Segments (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Segment Reporting Information [Line Items]
Net income (loss)	$ 349,984	$ 280,401	$ 984,543	$ 808,702
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	1,349,690	1,132,526	3,954,660	3,412,472
Business Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)	21,422	23,995	69,617	74,160
Business Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	116,513	112,650	344,562	332,341
Business Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total revenues	1,086	1,167	3,274	3,334
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)	102,796	108,422	309,515	312,926
Commercial Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	268,683	270,554	787,781	774,392
Commercial Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total revenues	950	1,097	2,917	3,281
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Net income (loss)	90,065	85,312	254,682	250,501
Commercial Real Estate [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	205,562	181,478	575,117	535,909
Commercial Real Estate [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total revenues	463	469	1,299	978
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Net income (loss)	50,773	5,113	151,522	21,823
Discretionary Portfolio [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	114,391	13,773	324,195	49,724
Discretionary Portfolio [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total revenues	(14,795)	(5,365)	(43,726)	(16,184)
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)	22,924	21,150	59,981	75,462
Residential Mortgage Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	108,576	99,518	309,393	310,843
Residential Mortgage Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total revenues	22,051	12,918	62,955	36,741
Retail Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)	69,506	64,721	204,291	202,415
Retail Banking [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	353,016	308,520	1,037,727	914,484
Retail Banking [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total revenues	3,052	3,292	9,198	9,688
All Other [Member]
Segment Reporting Information [Line Items]
Net income (loss)	(7,502)	(28,312)	(65,065)	(128,585)
All Other [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	182,949	146,033	575,885	494,779
All Other [Member] | Intersegment Activity Eliminated in Consolidated Totals [Member]
Segment Reporting Information [Line Items]
Total revenues	$ (12,807)	$ (13,578)	$ (35,917)	$ (37,838)