Derivatives (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Mar. 31, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Liabilities not subject to master netting agreements	$ 13,200				$ 13,200		$ 39,500
Derivative Assets not subject to master netting agreements	10,100				10,100		33,700
Collateral cash receivables	34,500				34,500		47,800
Collateral cash payables	28,200				28,200		32,800
Total trading revenues	45,000		$ 59,000		133,300	$ 185,900
Other Long-term Debt	1,059,507				1,059,507		1,040,656
Hedged amount of foreign currency denominated loans	1,300				1,300		3,800
Cash flow hedge length of time				5 years
Cash Flow Hedge | Hedged Items
Derivative Instruments, Gain (Loss) [Line Items]
Variability in Cash Flows Related to Debt Instruments (Primarily Loans)		$ 650,000		$ 250,000
Visa Class B Shares
Derivative Instruments, Gain (Loss) [Line Items]
Derivative liabilities related to sale	5,500				5,500		6,200
Long Term Debt Hedged With Fair Value Interest Rate Derivatives Using Long Haul Method
Derivative Instruments, Gain (Loss) [Line Items]
Net fair value of interest rate derivatives hedging subordinated debt	600				600		7,300
Other Long-term Debt	500,000				500,000		500,000
Long Term Debt Hedged With Fair Value Interest Rate Derivatives Using Long Haul Method | First Tennessee Bank National Association
Derivative Instruments, Gain (Loss) [Line Items]
Net fair value of interest rate derivatives hedging							1,600
Net fair value of interest rate derivatives hedging subordinated debt	200				200
Other Long-term Debt	400,000				400,000		400,000
Additional Derivative Agreements | Derivative Instruments With Accelerated Termination Provisions
Derivative Instruments, Gain (Loss) [Line Items]
Collateral received	113,600				113,600		137,500
Securities posted collateral	9,000				9,000		12,900
Net fair value of derivative assets with adjustable posting thresholds	27,400				27,400		35,900
Net fair value of derivative liabilities with adjustable posting thresholds	14,900				14,900		19,600
Additional Derivative Agreements | Derivative Instruments With Adjustable Collateral Posting Thresholds
Derivative Instruments, Gain (Loss) [Line Items]
Collateral received	113,600				113,600		137,600
Securities posted collateral	26,200				26,200		39,300
Net fair value of derivative assets with adjustable posting thresholds	27,400				27,400		35,900
Net fair value of derivative liabilities with adjustable posting thresholds	34,600				34,600		49,000
Interest Rate Contract | Cash Flow Hedge | Hedged Items
Derivative Instruments, Gain (Loss) [Line Items]
Variability in Cash Flows Related to Debt Instruments (Primarily Loans)	$ 900,000				$ 900,000		$ 250,000
Minimum
Derivative Instruments, Gain (Loss) [Line Items]
Cash flow hedge length of time		3 years
Maximum
Derivative Instruments, Gain (Loss) [Line Items]
Cash flow hedge length of time		7 years