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Investment Securities - Summary of Investment Securities (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Debt securities available for sale
Amortized Cost	$ 15,696	$ 11,295
Gross Unrealized Gain	88	39
Gross Unrealized Loss	732	932
Fair Value	15,052	10,402
Amortized cost of investment securities	2	3
Interest receivable	$ 43	$ 35
Debt Securities, Available-for-Sale, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration]	Other assets	Other assets
Asset Pledged as Collateral
Debt securities available for sale
Fair value	$ 14,800	$ 10,200
Mortgage-Related Debt Securities:
Debt securities available for sale
Amortized Cost	12,756	9,155
Gross Unrealized Gain	68	33
Gross Unrealized Loss	497	615
Fair Value	12,327	8,573
GSE CMOs
Debt securities available for sale
Amortized Cost	11,476	7,724
Gross Unrealized Gain	56	27
Gross Unrealized Loss	371	447
Fair Value	11,161	7,304
GSE certificates
Debt securities available for sale
Amortized Cost	1,130	1,273
Gross Unrealized Gain	1	0
Gross Unrealized Loss	126	167
Fair Value	1,005	1,106
Private label CMOs
Debt securities available for sale
Amortized Cost	150	158
Gross Unrealized Gain	11	6
Gross Unrealized Loss	0	1
Fair Value	161	163
Other Debt Securities:
Debt securities available for sale
Amortized Cost	2,940	2,140
Gross Unrealized Gain	20	6
Gross Unrealized Loss	235	317
Fair Value	2,725	1,829
GSE debentures
Debt securities available for sale
Amortized Cost	1,502	1,502
Gross Unrealized Gain	0	0
Gross Unrealized Loss	216	299
Fair Value	1,286	1,203
U. S. treasury obligations
Debt securities available for sale
Amortized Cost	1,000
Gross Unrealized Gain	14
Gross Unrealized Loss	0
Fair Value	1,014
Asset-backed securities
Debt securities available for sale
Amortized Cost	222	237
Gross Unrealized Gain	0	1
Gross Unrealized Loss	4	2
Fair Value	218	236
Corporate bonds
Debt securities available for sale
Amortized Cost	164	314
Gross Unrealized Gain	0	0
Gross Unrealized Loss	7	6
Fair Value	157	308
Capital trust notes
Debt securities available for sale
Amortized Cost	47	47
Gross Unrealized Gain	6	5
Gross Unrealized Loss	8	10
Fair Value	45	42
Foreign notes
Debt securities available for sale
Amortized Cost		35
Gross Unrealized Gain		0
Gross Unrealized Loss		0
Fair Value		35
Municipal bonds
Debt securities available for sale
Amortized Cost	5	5
Gross Unrealized Gain	0	0
Gross Unrealized Loss	0	0
Fair Value	$ 5	$ 5

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