Summary of Significant Accounting Policies - Schedule of Deferred Revenue Activity (Detail) - USD ($) $ in Millions |
12 Months Ended | |
|---|---|---|
Dec. 31, 2020 |
Dec. 31, 2019 |
|
| Accounting Policies [Abstract] | ||
| Deferred revenue on automotive sales with and without resale value guarantee— beginning of period | $ 1,472 | $ 883 |
| Additions | 724 | 880 |
| Net changes in liability for pre-existing contracts | 56 | 9 |
| Revenue recognized | (326) | (300) |
| Deferred revenue on automotive sales with and without resale value guarantee— end of period | $ 1,926 | $ 1,472 |