Fair Value Measurements - Level 3 Significant Unobservable Inputs (Detail) - Fair Value, Measurements, Recurring - Fair Value, Inputs, Level 3 - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Auction Rate
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
FAIR VALUE	$ 4.3	$ 4.7
Auction Rate \| Group One
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
VALUATION TECHNIQUE	Comparables	Comparables
Unobservable Inputs	Price	Price
Auction Rate \| Lower Limit
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial instrument price (in dollars per share)	$ 92	$ 84
Auction Rate \| Upper Limit
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial instrument price (in dollars per share)	$ 100	$ 99
Visa Conversion Rate Swap
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial liabilities, fair value	$ 29.7	$ 25.2
Visa Conversion Rate Swap \| Group One
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
VALUATION TECHNIQUE	Discounted Cash Flow	Discounted Cash Flow
Unobservable Inputs	Visa Class A Appreciation	Visa Class A Appreciation
Visa Conversion Rate Swap \| Group Two
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Unobservable Inputs	Conversion Rate	Conversion Rate
Visa Conversion Rate Swap \| Group Three
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Unobservable Inputs	Expected Duration	Expected Duration
Visa Conversion Rate Swap \| Lower Limit
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial instrument appreciation rate	7.00%	7.00%
Financial instruments conversion rate	1.63%	1.63%
Financial instrument, expected duration	1 year 6 months	1 year 6 months
Visa Conversion Rate Swap \| Upper Limit
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Financial instrument appreciation rate	11.00%	11.00%
Financial instruments conversion rate	1.65%	1.65%
Financial instrument, expected duration	4 years	4 years 6 months

Fair Value Assets And Liabilities Measured On Recurring Basis Significant Unobservable Inputs

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Financial Instruments Fair Value Assumptions Conversion Rate

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Financial Instruments Fair Value Assumptions Expected Conversion Rate

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Financial Instruments Fair Value Assumptions Price Per Share

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Financial Instruments Fair Value Assumptions Visa Class A Appreciation Percentage

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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Description of the inputs and valuation technique(s) used to measure fair value.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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Fair value of financial obligations, including, but not limited to, debt instruments, derivative liabilities, federal funds purchased and sold under agreements to repurchase, securities loaned or sold under agreements to repurchase, financial instruments sold not yet purchased, guarantees, line of credit, loans and notes payable, servicing liability, and trading liabilities.

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