Impaired Loans by Segment and Class (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013		Dec. 31, 2013
Financing Receivable, Impaired [Line Items]
Recorded Investment	$ 270.6				$ 270.6				$ 293.4
Unpaid principal balance	334.7				334.7				360.5
Specific allowance	8.5				8.5				10.4
Average recorded investment	278.2	[1]	281.2	[1]	286.3	[1]	270.0	[1]
Interest income recognized	0.9		1.2		1.9		2.0
Commercial
Financing Receivable, Impaired [Line Items]
Recorded Investment	90.0				90.0				99.5
Unpaid principal balance	106.1				106.1				123.2
Specific allowance	7.6				7.6				8.1
Average recorded investment	92.0	[1]	101.4	[1]	94.7	[1]	99.5	[1]
Interest income recognized	0.2		0.4		0.6		0.6
Commercial | Commercial and Institutional
Financing Receivable, Impaired [Line Items]
With no related specific reserve, recorded investment	12.6				12.6				12.2
With a related specific reserve, recorded investment	7.7				7.7				9.6
With no related specific reserve, unpaid principal balance	15.3				15.3				18.1
With a related specific reserve, unpaid principal balance	7.8				7.8				12.1
Specific allowance	3.7				3.7				3.6
With no related specific reserve, average recorded investment	10.6	[1]	10.8	[1]	11.0	[1]	11.5	[1]
With a related specific reserve, average recorded investment	9.7	[1]	12.5	[1]	9.9	[1]	11.7	[1]
With no related specific reserve, interest income recognized			0.1				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	49.7				49.7				46.6
With a related specific reserve, recorded investment	15.7				15.7				26.7
With no related specific reserve, unpaid principal balance	57.1				57.1				57.1
With a related specific reserve, unpaid principal balance	21.6				21.6				31.5
Specific allowance	3.9				3.9				4.5
With no related specific reserve, average recorded investment	44.7	[1]	40.3	[1]	44.8	[1]	40.0	[1]
With a related specific reserve, average recorded investment	22.7	[1]	33.2	[1]	24.6	[1]	31.7	[1]
With no related specific reserve, interest income recognized	0.2		0.2		0.5		0.4
With a related specific reserve, interest income recognized
Commercial | Lease Financing, net
Financing Receivable, Impaired [Line Items]
With no related specific reserve, recorded investment	4.3				4.3				4.4
With no related specific reserve, unpaid principal balance	4.3				4.3				4.4
With no related specific reserve, average recorded investment	4.3	[1]	4.6	[1]	4.4	[1]	4.6	[1]
With no related specific reserve, interest income recognized			0.1		0.1		0.1
Personal
Financing Receivable, Impaired [Line Items]
Recorded Investment	180.6				180.6				193.9
Unpaid principal balance	228.6				228.6				237.3
Specific allowance	0.9				0.9				2.3
Average recorded investment	186.2	[1]	179.8	[1]	191.6	[1]	170.5	[1]
Interest income recognized	0.7		0.8		1.3		1.4
Personal | Residential Real Estate
Financing Receivable, Impaired [Line Items]
With no related specific reserve, recorded investment	177.9				177.9				185.0
With a related specific reserve, recorded investment	1.4				1.4				8.1
With no related specific reserve, unpaid principal balance	225.8				225.8				227.8
With a related specific reserve, unpaid principal balance	1.5				1.5				8.7
Specific allowance	0.4				0.4				2.3
With no related specific reserve, average recorded investment	181.2	[1]	156.6	[1]	185.2	[1]	148.7	[1]
With a related specific reserve, average recorded investment	3.8	[1]	8.3	[1]	5.4	[1]	9.0	[1]
With no related specific reserve, interest income recognized	0.7		0.6		1.3		1.1
With a related specific reserve, interest income recognized
Personal | Private Client
Financing Receivable, Impaired [Line Items]
With no related specific reserve, recorded investment	0.4				0.4				0.8
With a related specific reserve, recorded investment	0.9				0.9
With no related specific reserve, unpaid principal balance	0.4				0.4				0.8
With a related specific reserve, unpaid principal balance	0.9				0.9
Specific allowance	0.5				0.5
With no related specific reserve, average recorded investment	0.7	[1]	13.3	[1]	0.7	[1]	11.4	[1]
With a related specific reserve, average recorded investment	0.5	[1]	1.6	[1]	0.3	[1]	1.4	[1]
With no related specific reserve, interest income recognized			0.2				0.3
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.