Reserves Textuals (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Reserves For Losses (Textuals) [Abstract]
Participation interests in Card Member receivables purchased from affiliates	$ 1,600.0	$ 4,300.0
Allowance for Card Member Receivables, Recoveries of Bad Debts	31.0	28.0
Allowance for Card Member Loans, Recoveries of Bad Debts	$ 0.3	$ 0.3

Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(4)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

Name:	us-gaap_AllowanceForLoanAndLeaseLossRecoveryOfBadDebts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration