Derivatives (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Collateral cash receivables	$ 77,600,000	$ 88,600,000	$ 77,600,000	$ 88,600,000
Collateral cash payables	42,100,000	47,400,000	42,100,000	47,400,000
Total trading revenues	$ 59,000,000	43,000,000	185,900,000	143,200,000
Noncallable senior debt maturing date	Dec. 15, 2020
Other Long-term Debt	$ 1,065,651,000	1,339,940,000	1,065,651,000	1,339,940,000	$ 1,312,677,000
Hedged amount of foreign currency denominated loans	2,600,000	2,800,000	2,600,000	2,800,000
Gain on extinguishment of debt	0	5,794,000	0	5,794,000
Visa Class B Shares [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative liabilities related to sale	$ 6,500,000	4,800,000	6,500,000	4,800,000
First Tennessee Bank National Association [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Noncallable senior debt maturing date	Dec. 01, 2019
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		6,100,000		6,100,000
Other Long-term Debt		250,000,000		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	$ 7,700,000	2,100,000	7,700,000	2,100,000
Other Long-term Debt	500,000,000	500,000,000	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	9,600,000	8,800,000	9,600,000	8,800,000
Other Long-term Debt	400,000,000	400,000,000	400,000,000	400,000,000
Subordinated Debentures Subject To Mandatory Redemption Amounts Redeemed [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Other Long-term Debt		200,000,000		200,000,000
Additional Derivative Agreements [Member] | Derivative Instruments With Accelerated Termination Provisions [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Collateral received	156,900,000	156,900,000	156,900,000	156,900,000
Securities posted collateral	28,400,000	24,600,000	28,400,000	24,600,000
Net fair value of derivative assets with adjustable posting thresholds	80,500,000	93,100,000	80,500,000	93,100,000
Net fair value of derivative liabilities with adjustable posting thresholds	23,800,000	20,200,000	23,800,000	20,200,000
Additional Derivative Agreements [Member] | Derivative Instruments With Adjustable Collateral Posting Thresholds [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Collateral received	156,900,000	156,900,000	156,900,000	156,900,000
Securities posted collateral	68,400,000	79,900,000	68,400,000	79,900,000
Net fair value of derivative assets with adjustable posting thresholds	80,800,000	93,100,000	80,800,000	93,100,000
Net fair value of derivative liabilities with adjustable posting thresholds	66,700,000	$ 79,700,000	66,700,000	$ 79,700,000
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		$ 250,000,000