Loans - Narrative (Details) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) loan_segment	Sep. 30, 2020 USD ($)	Dec. 31, 2020 loan_segment
Receivables [Abstract]
Number of portfolio segments \| loan_segment			3		3
Net gains (losses) on sales of loans and lending-related commitments	$ 31	$ 113	$ 225	$ (75)
Net gains (losses) on sales of loans	$ 30	$ 24	$ 211	$ (76)

The net gain (loss) resulting from a sale of loans, including adjustments to record loans classified as held-for-sale at the lower-of-cost-or-market and fair value adjustments to loan held for investment purposes.

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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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