Loans and Leases - Narrative (Details) $ in Millions	6 Months Ended	12 Months Ended
Jun. 30, 2019 USD ($) loan_segment loan	Dec. 31, 2018 USD ($) loan
Financing Receivable, Credit Quality Indicator [Line Items]
Number of loans and leases segments \| loan_segment	2
Loans and leases pledged as collateral	$ 7,670.0	$ 6,510.0
Number of loans on non-accrual status \| loan	0	0
Loans more than 90 days past due \| loan	0	0
Loans modified in troubled debt restructurings \| loan	0	0
Total loans and leases	$ 25,421.0	$ 25,789.0
Loans and leases, allowance for losses	72.0	67.0
Commercial and Financial
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases	24,257.0	24,915.0
Individually evaluated for impairment \| Commercial and Financial
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans and leases	14.0	$ 8.0
Loans and leases, allowance for losses	$ 2.9

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

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Loans And Leases Receivable, Number Of Loans And Leases Segments

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

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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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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.

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

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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.

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