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Commitments, Contingencies and Off-Balance Sheet Arrangements - Tax - advantaged Investments No Longer Held - Additional Information (Detail) $ in Millions | 12 Months Ended
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Dec. 31, 2017 USD ($)
Commitments and Contingencies Disclosure [Abstract] |
Income tax credits and adjustments | $ 108.0

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- Definition A credit or adjustment for government or taxing authority authorized decrease in taxes owed as a result of meeting certain tax policy conditions. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585 + Details
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