GM Financial Receivables and Transactions - Allowance for Loan Losses (Details) - GM Financial [Member] - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses at beginning of period	$ 1,966	$ 924	$ 944	$ 911
Provision for loan losses	327	179	793	354
Charge-offs	(273)	(279)	(613)	(588)
Recoveries	91	132	247	277
Effect of foreign currency	0	1	(61)	3
Allowance for loan losses at end of period	$ 2,111	$ 957	2,111	$ 957
Impact of Adoption ASU 2016-13 [Member]
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for loan losses at beginning of period			$ 801

Amount of gain (loss) from converting allowance reserve for credit loss to currency of reporting entity from amount denominated or measured in a different currency, which decreases (increases) the allowance for loan and lease losses.

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Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

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Amount of increase in allowance for credit loss on financing receivable from recovery.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of writeoff of financing receivable, charged against allowance for credit loss.

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Amount of expense related loan transactions, lease transactions, credit loss from transactions other than loan and lease transactions, and other loss based on assessment of uncollectability from the counterparty to reduce the account to their net realizable value.

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