Legal Proceedings - 10-K (Details) - USD ($) $ in Millions	1 Months Ended		12 Months Ended
	Feb. 29, 2020	Sep. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Jul. 31, 2019	Nov. 30, 2015	Apr. 30, 2015	Mar. 31, 2015
Loss Contingencies [Line Items]
Document Period End Date			Dec. 31, 2020
Legal Reserve | Maximum
Loss Contingencies [Line Items]
Loss Contingency, Range of Possible Loss, Portion Not Accrued			$ 100.0
Interchange Litigation
Loss Contingencies [Line Items]
Litigation Settlement Amount		$ 900.0	6,600.0
Payments for Legal Settlements		5,300.0	$ 700.0
Conditional Return of Legal Settlements Paid Maximum Amount		$ 700.0
Litigation Settlement, Trigger Percent of Opt Out by Class Members for Return of Portion of Settlement Payments		15.00%	15.00%
Interchange Litigation | Visa
Loss Contingencies [Line Items]
Litigation Settlement Amount		$ 600.0
Payments for Legal Settlements			$ 467.0
Conditional Return of Legal Settlements Paid Maximum Amount		$ 467.0
Jo Ann Howard Pc Et Al V Cassity Et Al
Loss Contingencies [Line Items]
Alleged Present And Future Losses			$ 600.0
Compensatory damages								$ 356.0
Punitive damages								$ 36.0
Prejudgement interests							$ 179.0
Reduced Compensatory Damages						$ 289.0
Jo Ann Howard Pc Et Al V Cassity Et Al | Pending Litigation
Loss Contingencies [Line Items]
Compensatory damages					$ 72.0
Punitive damages					15.0
Loss contingency, damages awarded, interest, value					$ 15.0
Increase (decrease) in damages awarded				$ 2.6
Loss contingency, damages awarded, value				$ 99.5
Loss contingency, damages sought, value	$ 7.0