Derivative and Hedging Activities - Company's Carrying Amounts on our Hedged Loans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Loans and leases	$ 819	$ 1,061	$ 2,519	$ 3,421
U. S. treasury obligations
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Carrying Amount of Hedged Items	1,015		1,015		$ 0
Cumulative Amount of Fair Value Hedging Adjustments	15		15		0
GSE CMOs
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Carrying Amount of Hedged Items	2,026		2,026		0
Cumulative Amount of Fair Value Hedging Adjustments	7		7		0
GSE debentures
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Carrying Amount of Hedged Items	1,287		1,287		0
Cumulative Amount of Fair Value Hedging Adjustments	11		11		0
Debt securities available-for-sale
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Carrying Amount of Hedged Items	4,328		4,328		0
Cumulative Amount of Fair Value Hedging Adjustments	33		33		0
Loans and leases held-for-investment
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Carrying Amount of Hedged Items	3,389		3,389		5,861
Cumulative Amount of Fair Value Hedging Adjustments	(6)		(6)		$ (18)
Loans and leases	$ 0	$ 0	$ 10	$ 24

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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FLAGSTAR BANK, NATIONAL ASSOCIATION 10-Q