Allowance for Credit Losses on Loans and Leases - Activity in the Allowance for Loan and Lease Losses (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	$ 1,201	$ 992	$ 992
Charge-offs	(124)	(91)
Recoveries	9	10
Provision for (recovery of) credit losses on loans and leases	82	304
Balance, end of period	1,168	1,215	1,201
Loans and Leases Held for Investment: \| Multi-family
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	639	307	307
Charge-offs	(80)	(11)	(308)
Recoveries	0	1
Provision for (recovery of) credit losses on loans and leases	50	172
Balance, end of period	609	469	639
Loans and Leases Held for Investment: \| Commercial real estate
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	304	402	402
Charge-offs	(2)	(64)	(466)
Recoveries	0	0
Provision for (recovery of) credit losses on loans and leases	(13)	144
Balance, end of period	289	482	304
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	39	47	47
Charge-offs	(1)	0	(8)
Recoveries	0	0
Provision for (recovery of) credit losses on loans and leases	(1)	(5)
Balance, end of period	37	42	39
Loans and Leases Held for Investment: \| Commercial and industrial
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Charge-offs	(34)		(136)
Other
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	68	105	105
Charge-offs	(7)	(5)
Recoveries	3	2
Provision for (recovery of) credit losses on loans and leases	2	(33)
Balance, end of period	66	69	68
Other \| Commercial and industrial
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	151	131	131
Charge-offs	(34)	(11)
Recoveries	6	7
Provision for (recovery of) credit losses on loans and leases	44	26
Balance, end of period	$ 167	$ 153	$ 151

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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- Definition

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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- Definition

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

+ References

No definition available.

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- Definition

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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- Definition

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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