Loans, Allowance for Loan Losses and Credit Quality - Additional Information (Details) $ in Millions	9 Months Ended
	Sep. 30, 2020 USD ($) Segment	Oct. 31, 2020 USD ($)
Financing Receivable Modifications [Line Items]
Number of primary loan portfolio segments | Segment	3
COVID-19
Financing Receivable Modifications [Line Items]
Loans placed under deferral plan	$ 131
Loans with deferrals of principal and interest for three months	114
Loans with deferrals of principal for six months	$ 17
COVID-19 | Subsequent Event
Financing Receivable Modifications [Line Items]
Loans receivable outstanding under loan deferral plan		$ 2
Minimum | COVID-19
Financing Receivable Modifications [Line Items]
Deferral term for principal and interest payments	90 days
Maximum | COVID-19
Financing Receivable Modifications [Line Items]
Deferral term for principal and interest payments	180 days