Commitments, Contingencies and Guarantees (Schedule of Merchant Chargeback Guarantee) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Merchant Chargeback Guarantees [Member]
Loss Contingencies [Line Items]
Aggregate sales transaction volume	[1]	$ 40,963	$ 38,759

[1] Represents transactions processed on the Discover Network for which a potential liability exists that, in aggregate, can differ from credit card sales volume.