Segment Disclosures (Schedule of Segment Disclosures) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Interest income		$ 2,982	$ 2,937
Interest expense		584	632
Net interest income		2,398	2,305
Provision for credit losses	[1],[2]	1,807	809	[3]
Other income		490	458
Other expense		1,159	1,024
(Loss) income before income taxes		(78)	930
Other [Member]
Segment Reporting Information [Line Items]
Interest income		107	133
Credit Card Loans [Member]
Segment Reporting Information [Line Items]
Interest income		2,416	2,362
Total Other Loans [Member] | Private Student Loans [Member]
Segment Reporting Information [Line Items]
Interest income		205	205
Total Other Loans [Member] | Personal Loans [Member]
Segment Reporting Information [Line Items]
Interest income		254	237
Operating Segments [Member] | Direct Banking [Member]
Segment Reporting Information [Line Items]
Interest income		2,982	2,937
Interest expense		584	632
Net interest income		2,398	2,305
Provision for credit losses		1,807	809	[3]
Other income		366	372
Other expense		1,118	989
(Loss) income before income taxes		(161)	879
Operating Segments [Member] | Direct Banking [Member] | Other [Member]
Segment Reporting Information [Line Items]
Interest income		107	133
Operating Segments [Member] | Direct Banking [Member] | Credit Card Loans [Member]
Segment Reporting Information [Line Items]
Interest income		2,416	2,362
Operating Segments [Member] | Direct Banking [Member] | Total Other Loans [Member] | Private Student Loans [Member]
Segment Reporting Information [Line Items]
Interest income		205	205
Operating Segments [Member] | Direct Banking [Member] | Total Other Loans [Member] | Personal Loans [Member]
Segment Reporting Information [Line Items]
Interest income		254	237
Operating Segments [Member] | Payment Services [Member]
Segment Reporting Information [Line Items]
Interest income		0	0
Interest expense		0	0
Net interest income		0	0
Provision for credit losses		0	0	[3]
Other income		124	86
Other expense		41	35
(Loss) income before income taxes		83	51
Operating Segments [Member] | Payment Services [Member] | Other [Member]
Segment Reporting Information [Line Items]
Interest income		0	0
Operating Segments [Member] | Payment Services [Member] | Credit Card Loans [Member]
Segment Reporting Information [Line Items]
Interest income		0	0
Operating Segments [Member] | Payment Services [Member] | Total Other Loans [Member] | Private Student Loans [Member]
Segment Reporting Information [Line Items]
Interest income		0	0
Operating Segments [Member] | Payment Services [Member] | Total Other Loans [Member] | Personal Loans [Member]
Segment Reporting Information [Line Items]
Interest income		$ 0	$ 0

[1] Prior to adoption of ASU No. 2016-13 on January 1, 2020, credit losses were estimated using the incurred loss approach.

[2] Prior to adoption of ASU No. 2016-13 on January 1, 2020, credit losses were estimated using the incurred loss approach.

[3] Prior to adoption of ASU No. 2016-13 on January 1, 2020, credit losses were estimated using the incurred loss approach.