Allowance for Credit Losses on Loans and Leases - Schedule of Activity in the Allowance for Loan and Lease Losses (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	$ 1,268	$ 594	$ 992	$ 393	$ 393
Adjustment for Purchased PCD Loans				13
Charge-offs	(260)	(26)	(705)	(35)
Recoveries	21	2	35	12
Provision for (recovery of) credit losses on loans and leases	235	49	942	236
Balance, end of period	1,264	619	1,264	619	992
Loans and Leases Held for Investment: \| Multi-family
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	618	192	307	178	178
Adjustment for Purchased PCD Loans				0
Charge-offs	(101)	(2)	(188)	(2)	(119)
Recoveries	3	0	4	0
Provision for (recovery of) credit losses on loans and leases	104	(6)	501	8
Balance, end of period	624	184	624	184	307
Loans and Leases Held for Investment: \| Commercial real estate
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	328	69	366	46	46
Adjustment for Purchased PCD Loans				0
Charge-offs	(110)	(13)	(411)	(14)	(56)
Recoveries	6	0	6	0
Provision for (recovery of) credit losses on loans and leases	68	64	331	88
Balance, end of period	292	120	292	120	366
Loans and Leases Held for Investment: \| One-to-four family first mortgage
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	40	45	47	46	46
Adjustment for Purchased PCD Loans				0
Charge-offs	(7)	(1)	(8)	(3)	(3)
Recoveries	5	0	5	0
Provision for (recovery of) credit losses on loans and leases	4	(1)	(2)	0
Balance, end of period	42	43	42	43	47
Loans and Leases Held for Investment: \| Acquisition, development, and construction
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	43	23	36	20	20
Adjustment for Purchased PCD Loans				0
Charge-offs	(4)	0	(4)	0	0
Recoveries	0	0	0	0
Provision for (recovery of) credit losses on loans and leases	11	8	18	11
Balance, end of period	50	31	50	31	36
Other
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	239	265	236	103	103
Adjustment for Purchased PCD Loans				13
Charge-offs	(38)	(10)	(94)	(16)
Recoveries	7	2	20	12
Provision for (recovery of) credit losses on loans and leases	48	(16)	94	129
Balance, end of period	$ 256	$ 241	$ 256	$ 241	$ 236

Amount excluding accrued interest, of allowance for credit loss on financing receivable. Excludes net investment in lease.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479344/326-20-45-1

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Amount, excluding accrued interest, of increase in allowance for credit loss on financing receivable from recovery. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount, excluding accrued interest, of decrease in allowance for credit loss on financing receivable from writeoff. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-6

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

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Amount, excluding accrued interest, of credit loss expense (reversal of expense) on financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

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Amount, excluding accrued interest, of allowance for credit loss at acquisition date of financing receivable purchased with credit deterioration. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 19
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-19

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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-SubTopic 20
-Name Accounting Standards Codification
-Section 50
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

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