Derivatives (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2016	Sep. 30, 2015	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Collateral cash receivables	$ 90,000		$ 80,600	$ 90,000	$ 80,600
Collateral cash payables	42,800		41,100	42,800	41,100
Total trading revenues	$ 69,300		46,700	126,900	100,200
Noncallable senior debt maturing date	Dec. 15, 2020
Other Long-term Debt	$ 1,076,943		1,555,272	1,076,943	1,555,272	$ 1,312,677
Hedged amount of foreign currency denominated loans	1,500		3,500	1,500	3,500
Gains/(loss) on extinguishment of debt	0	$ 5,800
Visa Class B Shares [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative liabilities related to sale	$ 6,800		4,800	6,800	4,800
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			9,100		9,100
Other Long-term Debt			250,000		250,000
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	$ 11,600		4,500	11,600	4,500
Other Long-term Debt	500,000		500,000	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	12,900		2,300	12,900	2,300
Other Long-term Debt	400,000		400,000	400,000	400,000
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			5,100		5,100
Other Long-term Debt			200,000		200,000
Additional Derivative Agreements [Member] | Derivative Instruments With Accelerated Termination Provisions [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Collateral received	168,000		144,200	168,000	144,200
Securities posted collateral	33,200		23,300	33,200	23,300
Net fair value of derivative assets with adjustable posting thresholds	94,600		72,500	94,600	72,500
Net fair value of derivative liabilities with adjustable posting thresholds	30,700		17,000	30,700	17,000
Additional Derivative Agreements [Member] | Derivative Instruments With Adjustable Collateral Posting Thresholds [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Collateral received	168,000		144,200	168,000	144,200
Securities posted collateral	81,300		71,900	81,300	71,900
Net fair value of derivative assets with adjustable posting thresholds	95,000		72,500	95,000	72,500
Net fair value of derivative liabilities with adjustable posting thresholds	81,300		$ 71,600	81,300	$ 71,600
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			$ 250,000