Commitments - Extensions of Credit (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Extended lines of credit
Commitments, guarantees:
Unused amounts in lines of credit to third-party entities and commitments for future financing to clients	$ 7,902	$ 7,368
Financing for client purchase agreements
Commitments, guarantees:
Unused amounts in lines of credit to third-party entities and commitments for future financing to clients	$ 4,165	$ 4,432

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