Loans and Leases - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended			6 Months Ended										6 Months Ended		12 Months Ended		6 Months Ended	12 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013	Jun. 30, 2014 Lower Limit	Jun. 30, 2014 Upper Limit	Jun. 30, 2014 First Lien	Dec. 31, 2013 First Lien	Jun. 30, 2014 Equity	Dec. 31, 2013 Equity	Jun. 30, 2014 Nonperforming Financing Receivable	Dec. 31, 2013 Nonperforming Financing Receivable	Jun. 30, 2014 Performing Financing Receivable	Dec. 31, 2013 Performing Financing Receivable	Jun. 30, 2014 Performing Financing Receivable Lower Limit	Jun. 30, 2014 Residential Real Estate Re-Defaulted	Mar. 31, 2014 Residential Real Estate Re-Defaulted Loan	Mar. 31, 2013 Residential Real Estate Re-Defaulted Loan	Jun. 30, 2014 Private Client Re-Defaulted	Mar. 31, 2014 Private Client Re-Defaulted Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collateral required on Residential real estate loan, lower limit	65.00%		65.00%
Collateral required on Residential real estate loan, upper limit	80.00%		80.00%
Draw period for credit line products			10 years
Equity credit lines										$ 1,900,000,000	$ 2,000,000,000
Loans held by Northern trust								87.00%	87.00%
Other U.S. loans and non-U.S. loans, short duration advances	1,900,000,000		1,900,000,000		1,300,000,000
Demand deposits	83,900,000		83,900,000		104,100,000
Loans held for sale	9,500,000		9,500,000		0
Days contractually past due for interest and principal and the loan is not well-secured and in the process of collection						90 days
Number of days past due for disclosure purposes to be categorized as a current							29 days
Maximum limit of individual homogeneous loans collective evaluation for impairment and excluded from impaired loan disclosures	250,000		250,000
Interest income that would have been recorded for nonperforming loans	2,400,000	2,600,000	4,900,000	5,200,000
Undrawn loan commitments and standby letters of credit	1,500,000		1,500,000		3,400,000
Total Loans and Leases	30,697,600,000		30,697,600,000		29,385,500,000							62,800,000	72,700,000	91,900,000	89,800,000
Period for which troubled debt restructurings with modified terms is performing before ceasing to be classified as impaired loan																6 months
Troubled debt restructuring loans and leases receivable to Performing status																6 months
Number of Loans and Leases																		3	0		1
Recorded Investment																	487,400			5,000
Unpaid Principal Balance																	$ 862,700			$ 5,000