Business Segments - Additional Information (Detail) (USD $)
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12 Months Ended | ||
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Dec. 31, 2014
Segment
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Dec. 31, 2013
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Dec. 31, 2012
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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 | 3,800,000,000 | $ 3,700,000,000 | $ 3,200,000,000 |
Total non-fiduciary assets of the trust and investment services segment | 4,000,000 | $ 3,900,000 | $ 2,800,000 |