Allowances for Credit Losses and Recorded Investments in Loans and Leases by Segment (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Loans and Leases
Specifically Evaluated for Impairment	$ 156.1	$ 157.3
Evaluated for Inherent Impairment	33,666.0	33,023.6
Total Loans and Leases	33,822.1	33,180.9
Allowance for Credit Losses on Credit Exposures
Specifically Evaluated for Impairment	2.1	3.1
Evaluated for Inherent Impairment	158.9	190.7
Allowance Assigned to Loans and Leases	161.0	193.8	$ 267.0
Allowance for Undrawn Exposures
Commitments and Standby Letters of Credit	31.0	39.5	28.9
Total Allowance for Credit Losses	192.0	233.3	295.9	$ 307.9
Personal
Loans and Leases
Specifically Evaluated for Impairment	109.2	101.0
Evaluated for Inherent Impairment	17,810.6	17,923.4
Total Loans and Leases	17,919.8	18,024.4
Allowance for Credit Losses on Credit Exposures
Specifically Evaluated for Impairment	2.1	0.1
Evaluated for Inherent Impairment	75.2	107.4
Allowance Assigned to Loans and Leases	77.3	107.5	123.2
Allowance for Undrawn Exposures
Commitments and Standby Letters of Credit	9.8	11.0	3.0
Total Allowance for Credit Losses	87.1	118.5	126.2	139.9
Commercial
Loans and Leases
Specifically Evaluated for Impairment	46.9	56.3
Evaluated for Inherent Impairment	15,855.4	15,100.2
Total Loans and Leases	15,902.3	15,156.5
Allowance for Credit Losses on Credit Exposures
Specifically Evaluated for Impairment	0.0	3.0
Evaluated for Inherent Impairment	83.7	83.3
Allowance Assigned to Loans and Leases	83.7	86.3	143.8
Allowance for Undrawn Exposures
Commitments and Standby Letters of Credit	21.2	28.5	25.9
Total Allowance for Credit Losses	$ 104.9	$ 114.8	$ 169.7	$ 168.0

Allowance for Undrawn Exposure [Abstract]

No definition available.

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- Definition

This represents total allowance for credit losses established to cover probable credit losses related to loans and leases as well as off-balance sheet instruments including unfunded commitments and standby letters of credit. This differs from the US XBRL taxonomy tag in that the taxonomy tag does not include the allowance for off-balance sheet instruments in its scope.

+ References

No definition available.

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- Definition

Reflects the allowance for credit losses assigned to unfunded commitments and standby letters of credit as of the balance sheet date.

+ References

No definition available.

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- References

No definition available.

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- Definition

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

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- Definition

Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

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- Definition

The balance of financing receivables that were collectively evaluated for impairment.

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- Definition

The balance of financing receivables that were individually evaluated for impairment.

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- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(d))
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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
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-URI http://asc.fasb.org/extlink&oid=65884687&loc=d3e4428-111522

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-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5074-111524

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- References

No definition available.

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