Loans (Narrative) (Details)		3 Months Ended		9 Months Ended
		Sep. 30, 2016 USD ($) number	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) number	Sep. 30, 2015 USD ($)	Sep. 16, 2016 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)	Oct. 02, 2015 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings loans		$ 289,600,000	$ 304,700,000	$ 289,600,000	$ 304,700,000
Allowance for loan losses		201,557,000	210,814,000	201,557,000	210,814,000		$ 199,807,000	$ 210,242,000		$ 221,351,000	$ 232,448,000
Average balance of impaired loans		312,649,000	337,301,000	313,034,000	343,935,000
Interest income recognized on impaired loan		1,760,000	1,718,000	4,898,000	5,086,000
Loans, net of unearned income	[1]	19,555,787,000	16,725,492,000	19,555,787,000	16,725,492,000			17,686,502,000
Provision for loan losses		4,000,000	1,000,000	11,000,000	8,000,000
Loan loss provision on PCI loans		300,000	100,000		(400,000)
Allowance - purchased credit impaired loans		1,166,000	2,919,000	1,166,000	2,919,000
As Acquired | Trustatlantic Financial Corporation
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired									$ 298,100,000
As Acquired | GE Capital Member
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired						$ 537,400,000
As Recorded by FHN | Trustatlantic Financial Corporation
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired									$ 281,900,000
Permanent Mortgage Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses		$ 16,589,000	20,076,000	$ 16,589,000	20,076,000		17,600,000	18,947,000		22,377,000	19,122,000
TDR, reduction of interest rate by increment, basis points		0.25%		0.25%
TDRS Maturities				40 years
Loans, net of unearned income		$ 436,100,000	463,893,000	$ 436,100,000	463,893,000			454,123,000
Modified interest rate increase		1.00%		1.00%
Provision for loan losses		$ (877,000)	(1,492,000)	$ (3,026,000)	2,467,000
Allowance - purchased credit impaired loans		0	0	0	0
Loans Held-For-Sale
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings loans		71,200,000	72,600,000	$ 71,200,000	72,600,000
Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk, percentage				26.00%
Consumer Real Estate Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk, percentage				23.00%
Allowance for loan losses		53,235,000	82,472,000	$ 53,235,000	82,472,000		59,081,000	80,614,000		85,457,000	113,011,000
TDRS Maturities				30 years
Loans, net of unearned income	[2]	4,578,371,000	4,813,936,000	$ 4,578,371,000	4,813,936,000			4,766,518,000
Provision for loan losses		(7,078,000)	(776,000)	(26,920,000)	(25,465,000)
Allowance - purchased credit impaired loans		333,000	504,000	333,000	504,000
Allowance For TDRs To Recorded Investment Of TDRs
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings loans		$ 48,700,000	$ 51,200,000	$ 48,700,000	$ 51,200,000
Ratio of the allowance for loan losses to loans		17.00%	17.00%	17.00%	17.00%
Loans To Mortgage Companies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage contributed in total loan		13.00%		13.00%
Percentage of commercial & industrial loan portfolio		20.00%		20.00%
Commercial loans		$ 2,479,819,000	$ 1,375,320,000	$ 2,479,819,000	$ 1,375,320,000
Loans, net of unearned income		2,479,819,000	1,375,320,000	2,479,819,000	1,375,320,000
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses		119,286,000	96,811,000	119,286,000	96,811,000
Average balance of impaired loans		56,199,000	59,714,000	53,084,000	62,614,000
Interest income recognized on impaired loan		309,000	276,000	740,000	841,000
Commercial loans		14,183,893,000	11,098,339,000	$ 14,183,893,000	11,098,339,000
Time period of default probability				1 year
Allowance - purchased credit impaired loans		833,000	2,414,000	$ 833,000	2,414,000
Credit Card & Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses		12,447,000	11,455,000	12,447,000	11,455,000		$ 11,890,000	11,885,000		$ 13,275,000	$ 14,730,000
Loans, net of unearned income		357,423,000	349,324,000	357,423,000	349,324,000			354,536,000
Provision for loan losses		3,240,000	666,000	8,217,000	7,256,000
Allowance - purchased credit impaired loans		$ 0	1,000	$ 0	1,000
Credit Card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit card workout program, granted rate reduction		0.00%		0.00%
Loans, net of unearned income		$ 189,176,000	190,990,000	$ 189,176,000	190,990,000
Heloc And Real Estate Installment Classes
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDR, reduction of interest rate by increment, basis points		0.25%		0.25%
Modified interest rate increase		2.00%		2.00%
Restricted And Secured Consumer Real Estate Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income		$ 38,500,000	59,300,000	$ 38,500,000	59,300,000			$ 52,800,000
Finance And Insurance Companies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage contributed in total loan		12.00%		12.00%
Percentage of commercial & industrial loan portfolio		19.00%		19.00%
Commercial loans		$ 2,300,000,000		$ 2,300,000,000
Finance Insurance And Loans To Mortgage Companies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of commercial & industrial loan portfolio		39.00%		39.00%
Maximum | Permanent Mortgage Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Modified interest rate time period				5 years
Maximum | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Forbearance agreements time period				12 months
Maximum | Credit Card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Payment reductions, time period				1 year
Credit card workout program, term extension				5 years
Maximum | Heloc And Real Estate Installment Classes
Accounts, Notes, Loans and Financing Receivable [Line Items]
Modified interest rate time period				5 years
Minimum | Permanent Mortgage Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Modified interest rate		2.00%		2.00%
Modified interest rate time period				5 years
Minimum | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Forbearance agreements time period				6 months
Minimum | Credit Card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Payment reductions, time period				6 months
Minimum | Heloc And Real Estate Installment Classes
Accounts, Notes, Loans and Financing Receivable [Line Items]
Modified interest rate		1.00%		1.00%
Modified interest rate time period				5 years
Pass | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades | number		12		12
Pass | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades | number		1		1
Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades | number		13		13
Special Mention | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades | number		13		13
Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades | number		14		14
Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades | number		15		15
Unlikely to be Collected Financing Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades | number		16		16
Unlikely to be Collected Financing Receivable | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades | number		16		16
PD Grade 1
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses		$ 85,000	127,000	$ 85,000	127,000
Lowest expected default probability | number		1		1
PD Grade 12
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses		$ 4,290,000	2,975,000	$ 4,290,000	2,975,000
PD Grade 13
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses		7,262,000	$ 4,256,000	7,262,000	$ 4,256,000
PD Grade 13 | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loans		$ 500,000		$ 500,000
LGD Grade 1 | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades | number		1		1
LGD Grade 12 | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades | number		12		12
Loan Reassessed | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loans		$ 1,000,000		$ 1,000,000

[1] September 30 , 2016 and 2015 and December 31, 2015 include $30.3 million, $30.7 million and $29.7 million, respectively, of held-to-maturity consumer mortgage loans secured by residential real estate properties in pr ocess of foreclosure.

[2] Balances as of September 3 0 , 2016 and 2015, and December 31, 2015, include $ 38.5 million, $ 59 . 3 million, and $ 52.8 million of restricted real estate loans, respectively. See Note 13 - Variable Interest Entities for additional information.