Segment Information - Summary of prior period financial information restated (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Segment Reporting Information [Line Items]
Net income (loss)	$ 241,613	$ 229,017
Business Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)	24,811	24,973
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)	96,423	98,841
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Net income (loss)	80,086	72,552
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Net income (loss)	5,954	11,360
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)	31,965	18,580
Retail Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)	68,888	69,034
All Other [Member]
Segment Reporting Information [Line Items]
Net income (loss)		(66,323)
Net income (loss) as previously reported [Member]
Segment Reporting Information [Line Items]
Net income (loss)		229,017
Net income (loss) as previously reported [Member] | Business Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)		28,598
Net income (loss) as previously reported [Member] | Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)		99,765
Net income (loss) as previously reported [Member] | Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Net income (loss)		74,561
Net income (loss) as previously reported [Member] | Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Net income (loss)		11,279
Net income (loss) as previously reported [Member] | Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)		19,411
Net income (loss) as previously reported [Member] | Retail Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)		29,711
Net income (loss) as previously reported [Member] | All Other [Member]
Segment Reporting Information [Line Items]
Net income (loss)		(34,308)
Impact of changes [Member] | Business Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)		(3,625)
Impact of changes [Member] | Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)		(924)
Impact of changes [Member] | Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Net income (loss)		(2,009)
Impact of changes [Member] | Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Net income (loss)		81
Impact of changes [Member] | Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)		(831)
Impact of changes [Member] | Retail Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)		39,323
Impact of changes [Member] | All Other [Member]
Segment Reporting Information [Line Items]
Net income (loss)		$ (32,015)