Fair Value of Financial Instruments - Fair Value Assets Measured on a Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Assets:
Beneficial interests in securitizations	$ 239	$ 131
Money market funds
Assets:
Money market funds	215	308
Level 1
Assets:
Beneficial interests in securitizations	0	0
Level 1 \| Money market funds
Assets:
Money market funds	215	308
Level 2
Assets:
Beneficial interests in securitizations	0	0
Level 2 \| Money market funds
Assets:
Money market funds	0	0
Level 3
Assets:
Beneficial interests in securitizations	239	131
Level 3 \| Money market funds
Assets:
Money market funds	$ 0	$ 0

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

No definition available.

Name:	us-gaap_CashAndCashEquivalentsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant