Derivatives (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Collateral cash receivables	$ 41,900		$ 47,800
Collateral cash payables	29,400		32,800
Total trading revenues	42,700	$ 57,600
Other Long-term Debt	1,035,036		1,040,656
Hedged amount of foreign currency denominated loans	$ 1,900		3,800
Cash flow hedge length of time		5 years
Maximum [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Cash flow hedge length of time	7 years
Minimum [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Cash flow hedge length of time	3 years
Cash Flow Hedge | Hedged Items [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Variability in Cash Flows Related to Debt Instruments (Primarily Loans)	$ 650,000	$ 250,000
Visa Class B Shares [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative liabilities related to sale	6,000		6,200
Long Term Debt Hedged With Fair Value Interest Rate Derivatives Using Long Haul Method [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net fair value of interest rate derivatives hedging	500
Net fair value of interest rate derivatives hedging subordinated debt			7,300
Other Long-term Debt	500,000		500,000
Long Term Debt Hedged With Fair Value Interest Rate Derivatives Using Long Haul Method [Member] | First Tennessee Bank National Association [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net fair value of interest rate derivatives hedging	300		1,600
Other Long-term Debt	400,000		400,000
Additional Derivative Agreements [Member] | Derivative Instruments With Accelerated Termination Provisions [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Collateral received	120,600		137,500
Securities posted collateral	10,000		12,900
Net fair value of derivative assets with adjustable posting thresholds	30,700		35,900
Net fair value of derivative liabilities with adjustable posting thresholds	19,200		19,600
Additional Derivative Agreements [Member] | Derivative Instruments With Adjustable Collateral Posting Thresholds [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Collateral received	121,200		137,600
Securities posted collateral	33,000		39,300
Net fair value of derivative assets with adjustable posting thresholds	31,300		35,900
Net fair value of derivative liabilities with adjustable posting thresholds	44,100		49,000
Interest Rate Contract [Member] | Cash Flow Hedge | Hedged Items [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Variability in Cash Flows Related to Debt Instruments (Primarily Loans)	$ 900,000		$ 250,000