Loans and Leases (Narrative) (Details)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019 USD ($) payment_period	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) payment_period	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($) Loan	Dec. 31, 2017 USD ($) Loan	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collateral required on Residential real estate loan, lower limit	65.00%		65.00%
Collateral required on Residential real estate loan, upper limit	80.00%		80.00%
Draw period for credit line products			10 years
Other U.S. loans and non-U.S. loans, short duration advances	$ 1,400,000,000		$ 1,400,000,000		$ 2,200,000,000
Demand deposits	8,100,000		8,100,000		152,500,000
Held for Sale	0		0
Interest income that would have been recorded for nonperforming loans	2,000,000.0	$ 2,000,000	3,900,000	$ 4,200,000
Undrawn loan commitments and standby letters of credit	9,200,000		9,200,000		12,600,000
Total loans and leases	30,982,300,000		$ 30,982,300,000		32,490,000,000.0
Performing status, minimum period of time			6 months
Recorded investment					4,600,000	$ 100,000	$ 4,600,000	$ 100,000
Consumer loans with carrying value collateralized by residential real estate property	17,800,000		$ 17,800,000
Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Held for Sale	0		0
Other Financing Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Held for Sale					0
Nonperforming Financing Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	67,300,000		67,300,000		64,600,000
Performing Financing Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	$ 27,900,000		$ 27,900,000		$ 35,200,000
Re-Defaulted | Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans and leases | Loan					2	1
Lower Limit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Days contractually past due for interest and principal and the loan is not well-secured and in the process of collection			90 days
Lower Limit | Performing Financing Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Period for which troubled debt restructurings with modified terms is performing before ceasing to be classified as impaired loan			6 months
Upper Limit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of payment periods | payment_period	6		6
Limit of individual homogeneous loans collective evaluation for impairment and excluded from impaired loan disclosures (less than)	$ 1,000,000		$ 1,000,000
Equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Equity credit lines	$ 487,000,000.0		$ 487,000,000.0		$ 655,500,000
Percentage of total equity credit lines	97.00%		97.00%		95.00%