Loans (Narrative) (Details)		3 Months Ended
		Mar. 31, 2016 USD ($) number	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)	Oct. 02, 2015 USD ($)	Dec. 31, 2014 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings loans		$ 289,000,000	$ 317,800,000
Allowance for loan losses		204,034,000	228,328,000	$ 210,242,000		$ 232,448,000
Average balance of impaired loans		310,405,000	345,864,000
Interest income recognized on impaired loan		$ 1,467,000	1,663,000
Forbearance agreements time period		6 months
Loans, net of unearned income	[1]	$ 17,574,994,000	16,732,123,000	17,686,502,000
Provision for loan losses		3,000,000	5,000,000
Loan loss provision on PCI loans			(200,000)
Allowance - purchased credit impaired loans		1,148,000	3,095,000
As Acquired | Trustatlantic Financial Corporation
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired					$ 298,100,000
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		$ 18,754,000	20,186,000	18,947,000		19,122,000
TDR, reduction of interest rate by increment, basis points		0.25%
TDRS Maturities		40 years
Loans, net of unearned income		$ 442,791,000	511,708,000	454,123,000
Modified interest rate increase		1.00%
Provision for loan losses		$ (860,000)	1,630,000
Allowance - purchased credit impaired loans		0	0
Loans Held-For-Sale
Accounts, Notes, Loans and Financing Receivable [Line Items]
Troubled debt restructurings loans		$ 76,400,000	78,000,000
Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk, percentage		29.00%
Consumer Real Estate Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk, percentage		27.00%
Allowance for loan losses		$ 67,321,000	109,245,000	80,614,000		113,011,000
TDRS Maturities		30 years
Loans, net of unearned income	[2]	$ 4,690,230,000	4,922,817,000	4,766,518,000
Provision for loan losses		(12,102,000)	47,000
Allowance - purchased credit impaired loans		725,000	490,000
Modified Loans Classified As A TDR
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses		$ 54,600,000	$ 62,100,000
Ratio of the allowance for loan losses to loans		19.00%	20.00%
Loans To Mortgage Companies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage contributed in total loan		9.00%
Concentration risk, percentage		15.00%
Commercial loans		$ 1,495,858,000	$ 1,641,672,000
Loans, net of unearned income		1,495,858,000	1,641,672,000
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses		106,513,000	85,317,000
Average balance of impaired loans		46,471,000	60,790,000
Interest income recognized on impaired loan		113,000	290,000
Commercial loans		$ 12,087,752,000	10,959,252,000
Time period of default probability		1 year
Allowance - purchased credit impaired loans		$ 422,000	2,605,000
Credit Card & Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses		11,446,000	13,580,000	11,885,000		$ 14,730,000
Loans, net of unearned income		354,221,000	338,346,000	354,536,000
Provision for loan losses		2,080,000	1,893,000
Allowance - purchased credit impaired loans		$ 1,000	0
Credit Card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit card workout program, granted rate reduction		0.00%
Loans, net of unearned income		$ 188,511,000	179,949,000
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%
Modified interest rate increase		2.00%
Restricted And Secured Consumer Real Estate Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans, net of unearned income		$ 47,800,000	71,600,000	$ 52,800,000
Finance And Insurance Companies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage contributed in total loan		12.00%
Concentration risk, percentage		21.00%
Commercial loans		$ 2,200,000,000
Finance Insurance And Loans To Mortgage Companies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage contributed in total loan		36.00%
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%
Modified interest rate time period		5 years
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%
Modified interest rate time period		5 years
Pass | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades | number		12
Pass | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades | number		1
Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades | number		13
Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades | number		14
Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades | number		15
Unlikely to be Collected Financing Receivable | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades | number		16
PD Grade 1
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses		$ 127,000	75,000
Lowest expected default probability | number		1
PD Grade 12
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses		$ 3,588,000	4,103,000
PD Grade 13
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses		4,056,000	$ 4,989,000
PD Grade 13 | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loans		$ 500,000
LGD Grade 1 | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades | number		1
LGD Grade 12 | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades | number		12
Loan Reassessed | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loans		$ 1,000,000

[1] March 31, 2016 and 2015 and December 31, 2015 include $31.2 million , $28.0 million and $29.7 million, respectively, of held-to-maturity consumer mortgage loans secured by residential real estate properties in process of foreclosure.

[2] Balances as of March 31, 2016 and 2015, and December 31, 2015, include $ 47.8 million , $ 71 . 6 million, and $ 52 .8 million of restricted real estate loans, respectively. See Note 13 - Variable Interest Entities for additional information.