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INVESTMENTS - Carrying Value and Fair Value of HTM Debt Securities by Contractual Maturity Dates (Details) - USD ($) $ in Millions	Sep. 30, 2025	Jun. 30, 2025	Dec. 31, 2024	Sep. 30, 2024	Jun. 30, 2024	Dec. 31, 2023
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Amortized cost, net	$ 197,092		$ 242,382
Held-to-maturity Securities, Debt Maturities, Fair Value;
Fair value	185,346		224,410
Allowance for credit losses on HTM debt securities	131	$ 136	137	$ 141	$ 99	$ 95
Mortgage-backed securities
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, amortized cost	166
After 1 but within 5 years, amortized cost	954
After 5 but within 10 years, amortized cost	1,167
After 10 years, amortized cost	66,289
Amortized cost, net	68,576		73,789
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	166
After 1 but within 5 years, fair value	931
After 5 but within 10 years, fair value	1,105
After 10 years, fair value	58,833
Fair value	61,035		63,359
U.S. treasury securities
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, amortized cost	21,941
After 1 but within 5 years, amortized cost	70,849
After 5 but within 10 years, amortized cost	0
After 10 years, amortized cost	0
Amortized cost, net	92,790		126,142
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	21,564
After 1 but within 5 years, fair value	67,488
After 5 but within 10 years, fair value	0
After 10 years, fair value	0
Fair value	89,052		119,208
State and municipal
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, amortized cost	23
After 1 but within 5 years, amortized cost	191
After 5 but within 10 years, amortized cost	2,211
After 10 years, amortized cost	6,226
Amortized cost, net	8,651		8,903
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	20
After 1 but within 5 years, fair value	190
After 5 but within 10 years, fair value	2,137
After 10 years, fair value	5,765
Fair value	8,112		8,262
Foreign government
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, amortized cost	173
After 1 but within 5 years, amortized cost	598
After 5 but within 10 years, amortized cost	0
After 10 years, amortized cost	0
Amortized cost, net	771		988
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	175
After 1 but within 5 years, fair value	619
After 5 but within 10 years, fair value	0
After 10 years, fair value	0
Fair value	794		$ 991
All other
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount;
Due within 1 year, amortized cost	0
After 1 but within 5 years, amortized cost	0
After 5 but within 10 years, amortized cost	5,159
After 10 years, amortized cost	21,145
Amortized cost, net	26,304
Held-to-maturity Securities, Debt Maturities, Fair Value;
Due within 1 year, fair value	0
After 1 but within 5 years, fair value	0
After 5 but within 10 years, fair value	5,165
After 10 years, fair value	21,188
Fair value	$ 26,353