SECURITIES - Schedule of Investments (Details) - USD ($) $ in Millions		Dec. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-Sale, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Fair Value	[1]	$ 29,777	$ 24,007
Debt Securities, Held-to-Maturity, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost	[1]	9,184	9,834
Gross Unrealized Gains		9	4
Gross Unrealized Losses		(843)	(796)
Fair Value	[1]	8,350	9,042
Total equity securities, at cost, Amortized Cost		869	1,058
Equity securities, at cost, Fair Value		869	1,058
Equity securities, Amortized Cost		173	153
Equity securities, Fair Value		173	153
Portfolio level basis adjustments excluded from amortized cost		60
Debt Securities
Debt Securities, Available-for-Sale, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost		31,729	26,458
Gross Unrealized Gains		71	11
Gross Unrealized Losses		(2,023)	(2,462)
Fair Value		29,777	24,007
U.S. Treasury and other
Debt Securities, Available-for-Sale, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost		4,493	3,678
Gross Unrealized Gains		26	1
Gross Unrealized Losses		(139)	(193)
Fair Value		4,380	3,486
State and political subdivisions
Debt Securities, Available-for-Sale, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost		1	2
Gross Unrealized Gains		0	0
Gross Unrealized Losses		0	0
Fair Value		1	2
Total mortgage-backed securities
Debt Securities, Available-for-Sale, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost		26,568	21,530
Gross Unrealized Gains		45	10
Gross Unrealized Losses		(1,881)	(2,227)
Fair Value		24,732	19,313
Debt Securities, Held-to-Maturity, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost		8,696	9,253
Gross Unrealized Gains		9	4
Gross Unrealized Losses		(818)	(751)
Fair Value		7,887	8,506
Federal agencies and U.S. government sponsored entities
Debt Securities, Available-for-Sale, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost		26,289	21,250
Gross Unrealized Gains		45	10
Gross Unrealized Losses		(1,857)	(2,198)
Fair Value		24,477	19,062
Debt Securities, Held-to-Maturity, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost		8,696	9,253
Gross Unrealized Gains		9	4
Gross Unrealized Losses		(818)	(751)
Fair Value		7,887	8,506
Other/non-agency
Debt Securities, Available-for-Sale, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost		279	280
Gross Unrealized Gains		0	0
Gross Unrealized Losses		(24)	(29)
Fair Value		255	251
Collateralized loan obligations
Debt Securities, Available-for-Sale, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost		667	1,248
Gross Unrealized Gains		0	0
Gross Unrealized Losses		(3)	(42)
Fair Value		664	1,206
Asset-backed securities
Debt Securities, Held-to-Maturity, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost		488	581
Gross Unrealized Gains		0	0
Gross Unrealized Losses		(25)	(45)
Fair Value		$ 463	$ 536

[1] Includes only collateral pledged by the Company where counterparties have the right to sell or pledge the collateral.