Derivatives (Narrative) (Details) - Derivative Contract Type [Domain] - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Jan. 31, 2015	Dec. 31, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Collateral cash receivables	$ 80,600,000	$ 101,600,000	$ 80,600,000	$ 101,600,000
Collateral cash payables	41,100,000	71,300,000	41,100,000	71,300,000
Total trading revenues	46,700,000	40,500,000	$ 100,200,000	90,100,000
Noncallable senior debt maturing date			Dec. 01, 2015
Other Long-term Debt	1,557,647,000	1,501,209,000	$ 1,557,647,000	1,501,209,000		$ 1,880,105,000
Hedged amount of foreign currency denominated loans	3,500,000	800,000	3,500,000	800,000
Borrowings matured					$ 304,000,000
Visa Class B Shares [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative liabilities related to sale	4,800,000	4,700,000	$ 4,800,000	4,700,000
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	9,100,000	28,100,000	$ 9,100,000	28,100,000
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	4,500,000	14,000,000	4,500,000	14,000,000
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	2,300,000		2,300,000
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	5,100,000	12,100,000	5,100,000	12,100,000
Other Long-term Debt	200,000,000	200,000,000	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	144,200,000	190,600,000	144,200,000	190,600,000
Securities posted collateral	23,300,000	28,800,000	23,300,000	28,800,000
Net fair value of derivative assets with adjustable posting thresholds	72,500,000	116,800,000	72,500,000	116,800,000
Net fair value of derivative liabilities with adjustable posting thresholds	17,000,000	23,200,000	17,000,000	23,200,000
Additional Derivative Agreements [Member] | Derivative Instruments With Adjustable Collateral Posting Thresholds [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Collateral received	144,200,000	190,600,000	144,200,000	190,600,000
Securities posted collateral	71,900,000	92,300,000	71,900,000	92,300,000
Net fair value of derivative assets with adjustable posting thresholds	72,500,000	116,800,000	72,500,000	116,800,000
Net fair value of derivative liabilities with adjustable posting thresholds	$ 71,600,000	$ 91,600,000	$ 71,600,000	$ 91,600,000