SECURITIES - Schedule of Investments (Details) - USD ($) $ in Millions		Mar. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-Sale, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Fair Value	[1]	$ 31,187	$ 29,777
Debt Securities, Held-to-Maturity, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost	[1]	9,054	9,184
Gross Unrealized Gains		2	9
Gross Unrealized Gains		(924)	(843)
Fair Value		8,132	8,350
Total equity securities, at cost, Amortized Cost		791	869
Equity securities, at cost, fair value		791	869
Equity Securities, Amortized Cost		178	173
Equity Securities, Fair Value		178	173
Portfolio level basis adjustments excluded from amortized cost		(74)	60
Total debt securities available for sale, at fair value
Debt Securities, Available-for-Sale, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost		33,505	31,729
Gross Unrealized Gains		35	71
Gross Unrealized Losses		(2,353)	(2,023)
Fair Value		31,187	29,777
U.S. Treasury and other
Debt Securities, Available-for-Sale, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost		4,944	4,493
Gross Unrealized Gains		8	26
Gross Unrealized Losses		(182)	(139)
Fair Value		4,770	4,380
State and political subdivisions
Debt Securities, Available-for-Sale, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost		1	1
Gross Unrealized Gains		0	0
Gross Unrealized Losses		0	0
Fair Value		1	1
Total mortgage-backed securities
Debt Securities, Available-for-Sale, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost		28,267	26,568
Gross Unrealized Gains		26	45
Gross Unrealized Losses		(2,171)	(1,881)
Fair Value		26,122	24,732
Debt Securities, Held-to-Maturity, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost		8,587	8,696
Gross Unrealized Gains		1	9
Gross Unrealized Gains		(906)	(818)
Fair Value		7,682	7,887
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		27,989	26,289
Gross Unrealized Gains		26	45
Gross Unrealized Losses		(2,150)	(1,857)
Fair Value		25,865	24,477
Debt Securities, Held-to-Maturity, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost		8,587	8,696
Gross Unrealized Gains		1	9
Gross Unrealized Gains		(906)	(818)
Fair Value		7,682	7,887
Other/non-agency
Debt Securities, Available-for-Sale, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost		278	279
Gross Unrealized Gains		0	0
Gross Unrealized Losses		(21)	(24)
Fair Value		257	255
Collateralized loan obligations
Debt Securities, Available-for-Sale, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost		293	667
Gross Unrealized Gains		1	0
Gross Unrealized Losses		0	(3)
Fair Value		294	664
Asset-backed securities
Debt Securities, Held-to-Maturity, Fair Value to Amortized Cost, after Allowance for Credit Loss [Abstract]
Amortized Cost		467	488
Gross Unrealized Gains		1	0
Gross Unrealized Gains		(18)	(25)
Fair Value		$ 450	$ 463

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