Components of Other Comprehensive Income (Loss) - Schedule of Changes in AOCI (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance		$ 8,307	$ 5,076	$ 4,786
Net unrealized gains (losses)		(149)	92	126
Amounts reclassified from AOCI		1	7	11
Other comprehensive income (loss)		(148)	99	137
Ending balance		8,494	8,307	5,076
Accumulated Other Comprehensive Income (Loss)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	[1]	(140)	(239)	(376)
Other comprehensive income (loss)	[1]	(148)	99	137
Ending balance	[1]	(288)	(140)	(239)
Securities AFS
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance		108	31	(76)
Net unrealized gains (losses)		(144)	74	107
Amounts reclassified from AOCI		0	3	0
Other comprehensive income (loss)		(144)	77	107
Ending balance		(36)	108	31
Cash Flow Hedges
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance		12	3	(12)
Net unrealized gains (losses)		(3)	15	11
Amounts reclassified from AOCI		(7)	(6)	4
Other comprehensive income (loss)		(10)	9	15
Ending balance		2	12	3
Pension and Post-retirement Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance		(260)	(273)	(288)
Net unrealized gains (losses)		(2)	3	8
Amounts reclassified from AOCI		8	10	7
Other comprehensive income (loss)		6	13	15
Ending balance		$ (254)	$ (260)	$ (273)

[1] Due to the nature of the preferred stock issued by FHN and its subsidiaries, all components of other comprehensive income (loss) have been attributed solely to FHN as the controlling interest holder.