Fair Value of financial instruments- Additional Information (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Letter Of Credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fair Value Disclosure Off balance Sheet Risks Face Amount Asset	$ 63	$ 78
Commitments To Extend Credit
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Fair Value Disclosure Off balance Sheet Risks Face Amount Asset	$ 9,000	$ 8,400

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_FairValueOffBalanceSheetRisksDisclosureInformationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration