Loans and Leases - Narrative (Details)	3 Months Ended	12 Months Ended
Mar. 31, 2019 USD ($) loan_segment loan	Dec. 31, 2018 USD ($) loan
Financing Receivable, Recorded Investment [Line Items]
Number of loans and leases segments \| loan_segment	2
Loans and leases pledged as collateral	$ 7,200,000,000	$ 6,500,000,000
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	$ 23,381,000,000	$ 25,789,000,000
Commercial and Financial
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	22,405,000,000	24,915,000,000
Individually evaluated for impairment
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	$ 0
Individually evaluated for impairment \| Commercial and Financial
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases		$ 8,000,000

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

Loans And Leases Receivable, Number Of Loans And Leases Segments

+ 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://fasb.org/us-gaap/role/ref/legacyRef
-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.

+ References

No definition available.

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- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522

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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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66007379&loc=d3e113888-111728

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5086-111524

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