Business Segments - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015 Segment	Mar. 31, 2014
Segment Reporting Information [Line Items]
Operating segments	2
Trust and Investment Services [Member]
Segment Reporting Information [Line Items]
Market value of assets held by trust and investment services segment	3,900,000,000	$ 3,800,000,000
Total non-fiduciary assets of the trust and investment services segment	3,700,000	$ 4,000,000