Investment Securities (Schedule Of FHN's Investment Securities) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 4,861,393
Fair Value	4,724,411	$ 5,170,255
Pledged available for sale securities	3,700,000	4,000,000
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	10,000	10,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(214)	(99)
Fair Value	9,786	9,901
FHLB-Cincinnati
Schedule of Available-for-sale Securities [Line Items]
Restricted investments		87,900
FRB
Schedule of Available-for-sale Securities [Line Items]
Restricted investments		134,600
SBA-interest only strips
Schedule of Available-for-sale Securities [Line Items]
Fair Value	5,787	1,270
Corporates and other debt
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	10,000	10,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(214)	(99)
Fair Value	9,786	9,901
U.S. treasuries
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	100	100
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(2)	(1)
Fair Value	98	99
Government agency issued mortgage-backed securities (“MBS”)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,564,334	2,580,442
Gross Unrealized Gains	4,524	10,538
Gross Unrealized Losses	(74,558)	(13,604)
Fair Value	2,494,300	2,577,376
Government agency issued collateralized mortgage obligations (“CMO”)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,180,120	2,302,439
Gross Unrealized Gains	395	1,691
Gross Unrealized Losses	(72,935)	(34,272)
Fair Value	2,107,580	2,269,858
Other U.S. government agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	54,797	265,863
Gross Unrealized Gains	0	7
Gross Unrealized Losses	(395)	0
Fair Value	54,402	265,870
Corporates and other debt
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	55,609	55,799
Gross Unrealized Gains	488	23
Gross Unrealized Losses	(259)	(40)
Fair Value	55,838	55,782
States and municipalities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,433
Gross Unrealized Gains	3
Gross Unrealized Losses	(30)
Fair Value	6,406
Securities available-for-sale
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,861,393	5,204,643
Gross Unrealized Gains	5,410	12,259
Gross Unrealized Losses	(148,179)	(47,917)
Fair Value	$ 4,718,624	$ 5,168,985

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

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