Deposits (Narrative) (Details)	3 Months Ended
Mar. 31, 2020 channels
Deposits [Abstract]
Deposits source channels (in number of channels)	2

number of major channels through which the company offers its deposits

No definition available.

Name:	dfs_DepositsSourceChannels
Namespace Prefix:	dfs_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration