Finance Receivables - New Volume of TDR HFI & HFS Finance Receivables (Details) - Personal Loans $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) account	Sep. 30, 2019 USD ($) account	Sep. 30, 2020 USD ($) account	Sep. 30, 2019 USD ($) account
Financing Receivable, Troubled Debt Restructuring [Line Items]
Pre-modification TDR net finance receivables	$ 105	$ 129	$ 392	$ 373
Total post-modification TDR net finance receivables	$ 105	$ 129	$ 392	$ 373
Number of TDR accounts | account	13,581	18,545	52,780	55,358
Rate reduction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total post-modification TDR net finance receivables	$ 67	$ 86	$ 242	$ 257
Other
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total post-modification TDR net finance receivables	$ 38	$ 43	$ 150	$ 116