Impaired Loans by Segment and Class (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013		Dec. 31, 2013
Financing Receivable, Impaired [Line Items]
Recorded Investment	$ 302.4				$ 293.4
Unpaid principal balance	367.4				360.5
Specific allowance	11.8				10.4
Average recorded investment	294.1	[1]	259.1	[1]
Interest income recognized	1.0		0.8
Commercial
Financing Receivable, Impaired [Line Items]
Recorded Investment	105.7				99.5
Unpaid principal balance	123.9				123.2
Specific allowance	9.7				8.1
Average recorded investment	97.0	[1]	97.8	[1]
Interest income recognized	0.4		0.2
Commercial | Commercial and Institutional
Financing Receivable, Impaired [Line Items]
With no related specific reserve, recorded investment	12.2				12.2
With a related specific reserve, recorded investment	12.3				9.6
With no related specific reserve, unpaid principal balance	15.4				18.1
With a related specific reserve, unpaid principal balance	13.0				12.1
Specific allowance	3.7				3.6
With no related specific reserve, average recorded investment	11.4	[1]	12.2	[1]
With a related specific reserve, average recorded investment	10.0	[1]	11.0	[1]
With a related specific reserve, interest income recognized
Commercial | Commercial Real Estate
Financing Receivable, Impaired [Line Items]
With no related specific reserve, recorded investment	49.8				46.6
With a related specific reserve, recorded investment	27.0				26.7
With no related specific reserve, unpaid principal balance	58.1				57.1
With a related specific reserve, unpaid principal balance	33.0				31.5
Specific allowance	6.0				4.5
With no related specific reserve, average recorded investment	44.8	[1]	39.6	[1]
With a related specific reserve, average recorded investment	26.4	[1]	30.4	[1]
With no related specific reserve, interest income recognized	0.3		0.2
With a related specific reserve, interest income recognized
Commercial | Lease Financing, net
Financing Receivable, Impaired [Line Items]
With no related specific reserve, recorded investment	4.4				4.4
With no related specific reserve, unpaid principal balance	4.4				4.4
With no related specific reserve, average recorded investment	4.4	[1]	4.6	[1]
With no related specific reserve, interest income recognized	0.1
Personal
Financing Receivable, Impaired [Line Items]
Recorded Investment	196.7				193.9
Unpaid principal balance	243.5				237.3
Specific allowance	2.1				2.3
Average recorded investment	197.1	[1]	161.3	[1]
Interest income recognized	0.6		0.6
Personal | Residential Real Estate
Financing Receivable, Impaired [Line Items]
With no related specific reserve, recorded investment	190.7				185.0
With a related specific reserve, recorded investment	5.1				8.1
With no related specific reserve, unpaid principal balance	237.3				227.8
With a related specific reserve, unpaid principal balance	5.3				8.7
Specific allowance	1.7				2.3
With no related specific reserve, average recorded investment	189.2	[1]	141.0	[1]
With a related specific reserve, average recorded investment	7.1	[1]	9.8	[1]
With no related specific reserve, interest income recognized	0.6		0.5
With a related specific reserve, interest income recognized
Personal | Private Client
Financing Receivable, Impaired [Line Items]
With no related specific reserve, recorded investment	0.5				0.8
With a related specific reserve, recorded investment	0.4
With no related specific reserve, unpaid principal balance	0.5				0.8
With a related specific reserve, unpaid principal balance	0.4
Specific allowance	0.4
With no related specific reserve, average recorded investment	0.7	[1]	9.4	[1]
With a related specific reserve, average recorded investment	0.1	[1]	1.1	[1]
With no related specific reserve, interest income recognized			0.1
With a related specific reserve, interest income recognized

[1] Average recorded investment in impaired loans is calculated as the average of the month-end impaired loan balances for the period.