Allowance for Credit Losses on Loans and Leases - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Valuation Allowance [Line Items]
Allowance for credit losses on loans and leases	$ 200	$ 188	$ 200	$ 188	$ 194	$ 148
Increase in allowance for credit losses on loans and leases			$ 13	2
COVID-19 pandemic, impacts			For the nine months ended September 30, 2021, the allowance for credit losses on loan and leases increased primarily as a result of growth across segments of the loan portfolio, and by macroeconomic factors surrounding the COVID-19 pandemic, specifically the resultant estimated decreases in property values in the New York City area. The macroeconomic forecast includes Gross Domestic Product (“GDP”) to rise at an annualized rate of 5.0% for 2021 as the economy begins to recover from the systemic disruptions of the COVID-19 pandemic. Unemployment continues to subside from the historic shock of 2020, but is not forecasted to return to pre-pandemic levels around 3.5% until 2023. The 10-year U.S. Treasury yield is expected to steadily increase over the next few years. Baa Corp-10 Year treasury spread widens slightly beginning in 2022 and levels off at 2.6% through 2023. In addition to these quantitative inputs, several qualitative factors were considered in increasing our allowance for loan and lease credit losses, including the risk that the economic decline proves to be more severe and/or prolonged than our baseline forecast.
Net recoveries	1	$ (13)	$ 1	$ (51)
Unfunded Loan Commitment
Valuation Allowance [Line Items]
Allowance for credit losses	12		12
CARES Act
Valuation Allowance [Line Items]
Allowance for credit losses on loans and leases	$ 200		200
Increase in allowance for credit losses on loans and leases			6
Net recoveries			$ 7