Derivatives (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Jan. 31, 2015	Dec. 31, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Collateral cash receivables	$ 88,600,000	$ 89,800,000	$ 88,600,000	$ 89,800,000
Collateral cash payables	47,400,000	68,100,000	47,400,000	68,100,000
Total trading revenues	43,000,000	41,200,000	$ 143,200,000	131,300,000
Noncallable senior debt maturing date			Dec. 01, 2015
Other Long-term Debt	1,341,186,000	1,491,138,000	$ 1,341,186,000	1,491,138,000		$ 1,880,105,000
Hedged amount of foreign currency denominated loans	2,800,000		2,800,000
Borrowings matured					$ 304,000,000
Gains/(loss) on extinguishment of debt	5,794,000	0	5,794,000	(4,350,000)
Visa Class B Shares [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative liabilities related to sale	4,800,000	7,600,000	$ 4,800,000	7,600,000
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	21,400,000	$ 6,100,000	21,400,000
Other Long-term Debt	250,000,000	554,000,000	250,000,000	554,000,000
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	2,100,000	11,300,000	2,100,000	11,300,000
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	8,800,000		8,800,000
Other Long-term Debt	400,000,000		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		9,800,000		9,800,000
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	191,500,000	156,900,000	191,500,000
Securities posted collateral	24,600,000	26,300,000	24,600,000	26,300,000
Net fair value of derivative assets with adjustable posting thresholds	93,100,000	104,700,000	93,100,000	104,700,000
Net fair value of derivative liabilities with adjustable posting thresholds	20,200,000	19,100,000	20,200,000	19,100,000
Additional Derivative Agreements [Member] | Derivative Instruments With Adjustable Collateral Posting Thresholds [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Collateral received	156,900,000	191,500,000	156,900,000	191,500,000
Securities posted collateral	79,900,000	80,600,000	79,900,000	80,600,000
Net fair value of derivative assets with adjustable posting thresholds	93,100,000	104,700,000	93,100,000	104,700,000
Net fair value of derivative liabilities with adjustable posting thresholds	$ 79,700,000	$ 77,600,000	$ 79,700,000	$ 77,600,000