Summary of Significant Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2025	Dec. 31, 2024
Disaggregation of Revenue [Line Items]
Prepaid merchant bookings	$ 320	$ 319
Deferred merchant bookings	11,140	8,517
Deferred revenue	164	164
Deferred Merchant Bookings
Disaggregation of Revenue [Line Items]
Deferred merchant bookings	10,000	7,600
Deferred merchant bookings recognized during period	6,400
Revenue recognized during period	948
Deferred Loyalty Rewards
Disaggregation of Revenue [Line Items]
Deferred merchant bookings	1,100	937
Revenue recognized during period	730
Deferred Revenue
Disaggregation of Revenue [Line Items]
Revenue recognized during period	121
Deferred revenue	$ 164	$ 164