Basis of Presentation (Details) $ in Millions	Apr. 26, 2021 USD ($) state branch productionOffice shares	Jun. 30, 2022 USD ($)	Dec. 31, 2021 USD ($)
Business Acquisition [Line Items]
Assets | $	$ 85,000	$ 24,899	$ 25,483
Number of traditional branches | branch	400
Number of states in which branches are located	9
Number of loan production offices | productionOffice	80
Number of states in which offices are located	28
NYCB
Business Acquisition [Line Items]
Common stock portion, number of Flagstar stock for each share of NYCB common stock (in shares) | shares	4.0151