Fair Value - Changes in FV under the FV Option (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Loans
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value gains (losses), net	$ (5)	$ (10)	$ 20	$ 141
Long-term debt
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value gains (losses), net	$ (89)	$ (574)	$ 284	$ (312)

For each line item in the statement of financial position, the amounts of gains and losses from fair value changes included in earnings.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14172-108612

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration