Commitments - Extensions of Credit (Details) - USD ($) $ in Billions	Mar. 31, 2021	Dec. 31, 2020
Extended lines of credit
Commitments, guarantees:
Unused amounts in lines of credit to third-party entities and commitments for future financing to clients	$ 1.6	$ 2.1
Financing for client purchase agreements
Commitments, guarantees:
Unused amounts in lines of credit to third-party entities and commitments for future financing to clients	$ 4.7	$ 5.2

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