Derivatives (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Mar. 31, 2017	Mar. 31, 2016	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Total trading revenues	$ 29,900	$ 45,600			$ 68,000	$ 88,300
Term borrowings	1,227,281				1,227,281		$ 1,218,097
Cash flow hedge length of time				5 years
Hedged amount of foreign currency denominated loans	6,400				6,400		1,500
Visa Class B Shares
Derivative Instruments, Gain (Loss) [Line Items]
Derivative liabilities related to sale	9,400				9,400		5,600
Cash Flow Hedges | Hedging Instruments
Derivative Instruments, Gain (Loss) [Line Items]
Variability in cash flows related to debt instruments (primarily loans)				$ 250,000
Notional amount			$ 650,000
Cash Flow Hedges | Hedging Instruments | Minimum
Derivative Instruments, Gain (Loss) [Line Items]
Initial duration			3 years
Cash Flow Hedges | Hedging Instruments | Maximum
Derivative Instruments, Gain (Loss) [Line Items]
Initial duration			7 years
Long Term Debt Hedged With Fair Value Interest Rate Derivatives Using Long Haul Method
Derivative Instruments, Gain (Loss) [Line Items]
Term borrowings	500,000				500,000
Net fair value of interest rate derivatives hedging	0				0		200
Derivative Instruments With Adjustable Collateral Posting Thresholds | Additional Derivative Agreements
Derivative Instruments, Gain (Loss) [Line Items]
Net fair value of derivative assets with adjustable posting thresholds	21,700				21,700		23,300
Net fair value of derivative liabilities with adjustable posting thresholds	52,400				52,400		34,500
Collateral received	108,700				108,700		119,300
Securities posted collateral	16,500				16,500		18,900
Derivative Instruments With Accelerated Termination Provisions | Additional Derivative Agreements
Derivative Instruments, Gain (Loss) [Line Items]
Net fair value of derivative assets with adjustable posting thresholds	18,500				18,500		22,800
Net fair value of derivative liabilities with adjustable posting thresholds	47,000				47,000		19,400
Collateral received	105,500				105,500		118,600
Securities posted collateral	15,000				15,000		6,700
FTBNA | Long Term Debt Hedged With Fair Value Interest Rate Derivatives Using Long Haul Method
Derivative Instruments, Gain (Loss) [Line Items]
Term borrowings	400,000				400,000
Net fair value of interest rate derivatives hedging	0				0		100
Certain Counterparties
Derivative Instruments, Gain (Loss) [Line Items]
Collateral cash receivables	80,500				80,500		60,300
Collateral cash payables	$ 98,800				$ 98,800		$ 49,700