Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2022 USD ($) Segment shares	Dec. 31, 2021 USD ($)		Dec. 31, 2020 USD ($)		Dec. 31, 2019 USD ($)	[1]
Significant Accounting Policies [Line Items]
Cash and cash equivalents, interest-bearing deposits in other financial institutions	$ 2,032,000,000	$ 2,211,000,000	[1]	$ 1,948,000,000	[1]	$ 742,000,000
Cash and cash equivalents, interest-bearing deposits in other financial institutions, Federal Reserve Bank of New York	837,000,000	1,700,000,000
Cash and cash equivalents, federal funds sold	0	0
Cash and cash equivalents, outstanding reverse repurchase agreements	793,000,000	406,000,000
Allowance for credit losses	23,000,000	12,000,000
Goodwill	$ 2,426,000,000	2,426,000,000
Number of operating segments | Segment	1
Number of reportable segments | Segment	1
Goodwill impairment	$ 0
Depreciation	18,000,000	21,000,000		24,000,000
Bank-owned life insurance	1,561,000,000	1,184,000,000
Bank-owned life insurance income	32,000,000	29,000,000		$ 32,000,000
Other real estate owned	8,000,000	3,000,000
Estimate fair value of mortgage loans	$ 10,000,000	2,000,000
Shares available for grant | shares	9,799,865
Restricted cash	$ 50,000,000
Commercial Real Estate
Significant Accounting Policies [Line Items]
Percentage of loan portfolio	70.50%
2020 Incentive Plan
Significant Accounting Policies [Line Items]
Shares available for grant | shares	5,774,229
Taxi Medallion Loans
Significant Accounting Policies [Line Items]
Other real estate owned	$ 4,000,000	$ 5,000,000
Flagstar
Significant Accounting Policies [Line Items]
Bank-owned life insurance	$ 373,000,000
Shares available for grant | shares	4,025,636
Premises
Significant Accounting Policies [Line Items]
Premises, furniture, fixtures, and equipment, estimated useful lives (in years)	20 years
Furniture, Fixtures and Equipment | Minimum
Significant Accounting Policies [Line Items]
Premises, furniture, fixtures, and equipment, estimated useful lives (in years)	3 years
Furniture, Fixtures and Equipment | Maximum
Significant Accounting Policies [Line Items]
Premises, furniture, fixtures, and equipment, estimated useful lives (in years)	10 years

[1] For further information on restricted cash, see Note 14 - Derivatives and Hedging Activities.