Derivative Instruments and Hedging Activities (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Noncash collateral placed with counterparties	$ 552	$ 384
Cash collateral placed with counterparties		2
Cash collateral received from counterparties	$ 20	$ 23

Cash Collateral Received From Counterparties, Excluding Collateral Associated With Repurchase Agreements

No definition available.

Name:	ally_CashCollateralReceivedFromCounterpartiesExcludingCollateralAssociatedWithRepurchaseAgreements
Namespace Prefix:	ally_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant