Loans and Leases - Narrative (Details)	12 Months Ended
Dec. 31, 2017 USD ($) loan	Dec. 31, 2016 USD ($) loan
Financing Receivable, Recorded Investment [Line Items]
Loans and leases pledged as collateral \| $	$ 1,900,000,000	$ 1,500,000,000
Number of impaired loans and leases \| loan	0
Allowance for loan and lease losses \| $	$ 54,000,000	$ 53,000,000
Loans modified in troubled debt restructurings \| loan	0	0
Loans more than 90 days past due \| loan	0	0
Commercial and Financial
Financing Receivable, Recorded Investment [Line Items]
Number of impaired loans and leases \| loan		1
Recorded Investment \| $		$ 15,000,000
Unpaid Principal Balance \| $		15,000,000
Interest Income Recognized \| $		0
Allowance for loan and lease losses \| $		$ 200,000
Number of loans on non-accrual status \| loan	0	1
Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Number of loans on non-accrual status \| loan		0

Financing Receivable Recorded Investment Equal To Greater Than 90 Day

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- Definition

Financing Receivable, Recorded Investment, Nonaccrual Status, Number of Loans

+ References

No definition available.

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- Definition

Impaired Financing Receivables, Number of Contracts

+ References

No definition available.

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- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953676-111524

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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- Definition

Amount of interest income, recognized on accrual basis, on financing receivables, for which there is a related allowance for credit losses and are recognized as impaired.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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- Definition

Amount of investment in impaired financing receivables for which there is a related allowance for credit losses.

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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Unpaid principal balance of impaired financing receivables for which there is a related allowance for credit losses.

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-Publisher FASB
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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

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- Definition

Carrying amount as of the balance sheet date of loans that have been pledged as collateral for borrowings. If the secured party has the right by contract or custom to sell or re-pledge the collateral, then the debtor reclassifies that asset and report that asset in its statement of financial position separately from other assets not so encumbered.

+ References

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