Summary of Significant Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Financing Receivable, Allowance for Credit Loss [Line Items]
Customer Reward Program	$ 6.2	$ 5.4
Loan origination fees and direct loan origination costs amortization period	12 months
Credit Card
Financing Receivable, Allowance for Credit Loss [Line Items]
Loan origination fees and direct loan origination costs amortization period	12 months
Amortization term of annual membership fees	12 months