Components of Other Comprehensive Income (Loss) - Schedule of Changes in AOCI (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance		$ 8,494	$ 8,307	$ 5,076
Net unrealized gains (losses)		(1,103)	(149)	92
Amounts reclassified from AOCI		23	1	7
Other comprehensive income (loss)		(1,080)	(148)	99
Ending balance		8,547	8,494	8,307
Accumulated Other Comprehensive Income (Loss)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	[1]	(288)	(140)	(239)
Other comprehensive income (loss)	[1]	(1,080)	(148)	99
Ending balance	[1]	(1,368)	(288)	(140)
Securities AFS
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance		(36)	108	31
Net unrealized gains (losses)		(937)	(144)	74
Amounts reclassified from AOCI		0	0	3
Other comprehensive income (loss)		(937)	(144)	77
Ending balance		(973)	(36)	108
Cash Flow Hedges
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance		2	12	3
Net unrealized gains (losses)		(144)	(3)	15
Amounts reclassified from AOCI		15	(7)	(6)
Other comprehensive income (loss)		(129)	(10)	9
Ending balance		(127)	2	12
Pension and Post-retirement Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance		(254)	(260)	(273)
Net unrealized gains (losses)		(22)	(2)	3
Amounts reclassified from AOCI		8	8	10
Other comprehensive income (loss)		(14)	6	13
Ending balance		$ (268)	$ (254)	$ (260)

[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.