Derivatives (Narrative) (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Collateral cash receivables	$ 81,400,000	$ 93,400,000
Collateral cash payables	41,700,000	56,800,000
Total trading revenues	57,600,000	53,500,000
Other Long-term Debt	1,323,749,000	1,570,646,000	$ 1,312,677,000
Hedged amount of foreign currency denominated loans	$ 1,900,000	3,800,000
Gains/(loss) on extinguishment of debt			$ 5,800,000
Cash flow hedge length of time	5 years
Visa Class B Shares [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative liabilities related to sale	$ 4,600,000	5,000,000
Long Term Debt Hedged With Fair Value Interest Rate Derivatives Using Shortcut Method [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net fair value of interest rate derivatives hedging		12,000,000
Other Long-term Debt	250,000,000
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	7,000,000	6,900,000
Other Long-term Debt	500,000,000	500,000,000
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	10,800,000	5,500,000
Other Long-term Debt	400,000,000
Subordinated Debentures Subject To Mandatory Redemption Amounts Redeemed [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net fair value of interest rate derivatives hedging subordinated debt		2,700,000
Other Long-term Debt		200,000,000
Additional Derivative Agreements [Member] | Derivative Instruments With Accelerated Termination Provisions [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Collateral received	168,900,000	173,500,000
Securities posted collateral	24,500,000	25,900,000
Net fair value of derivative assets with adjustable posting thresholds	86,800,000	107,300,000
Net fair value of derivative liabilities with adjustable posting thresholds	22,600,000	21,100,000
Additional Derivative Agreements [Member] | Derivative Instruments With Adjustable Collateral Posting Thresholds [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Collateral received	168,900,000	173,500,000
Securities posted collateral	72,700,000	84,700,000
Net fair value of derivative assets with adjustable posting thresholds	86,800,000	107,300,000
Net fair value of derivative liabilities with adjustable posting thresholds	74,700,000	$ 84,500,000
Trust Preferred Loans [Member] | Cash Flow Hedge | Hedged Items [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Hedged held-to-maturity trust preferred loans principal balance	$ 250,000,000