Basis of Presentation (Details) $ / shares in Units, $ in Millions			3 Months Ended		9 Months Ended
	Oct. 27, 2022 $ / shares	Apr. 26, 2021 USD ($) productionOffice branch state shares	Sep. 30, 2022 USD ($) $ / shares	Sep. 30, 2021 $ / shares	Sep. 30, 2022 USD ($) $ / shares	Sep. 30, 2021 $ / shares	Dec. 31, 2021 USD ($)
Business Acquisition [Line Items]
Assets | $		$ 85,000	$ 25,443		$ 25,443		$ 25,483
Number of traditional branches | branch		400
Number of states in which branches are located | state		9
Number of loan production offices | productionOffice		80
Number of states in which offices are located | state		28
Dividends declared (in dollars per share) | $ / shares			$ 0.06	$ 0.06	$ 0.18	$ 0.18
Subsequent event
Business Acquisition [Line Items]
Dividends declared (in dollars per share) | $ / shares	$ 2.50
NYCB
Business Acquisition [Line Items]
Common stock portion, number of Flagstar stock for each share of NYCB common stock (in shares) | shares		4.0151