Allowance for Credit Losses on Loans and Leases - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Valuation Allowance [Line Items]
ACL at acquisition	$ 393	$ 199	$ 194
Increase in allowance for credit losses on loans and leases	$ 11	15
COVID-19 pandemic, impacts	For the year ended December 31, 2022 the increase in the allowance for credit losses on loans and leases was primarily driven by a combination of increased loan balances as a result of the Flagstar acquisition and changes in the macroeconomic environment both on a spot and forecasted basis, specifically the inflationary pressures leading to sharp increases in interest rates and a slow-down of prepayment activity leading to longer weighted average lives on the balance sheet. In addition, the impact of the forecasted macroeconomic factors had resultant decreases on market level factors in Property Prices on the Multi-Family, Commercial Real Estate and 1-4 Family loan portfolios reflecting the changing economic landscape.
Provision for loan losses	$ 133	3	$ 62
Unfunded Loan Commitment
Valuation Allowance [Line Items]
Allowance for credit losses	23	$ 12
CARES Act
Valuation Allowance [Line Items]
ACL at acquisition	393
Increase in allowance for credit losses on loans and leases	194
Recoveries from credit losses	$ 4