Loan Receivables (Narrative) (Details) $ in Millions			3 Months Ended				6 Months Ended
	Mar. 31, 2020 USD ($)	Jan. 01, 2020 USD ($)	Jun. 30, 2020 USD ($)		Jun. 30, 2019 USD ($)		Jun. 30, 2020 USD ($) segment		Jun. 30, 2020 USD ($)		Jun. 30, 2019 USD ($)		Dec. 31, 2019 USD ($)		Mar. 31, 2019 USD ($)	[3]	Dec. 31, 2018 USD ($)	[3]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loan portfolio segments (in segments) | segment							2
Allowance for credit losses	$ 6,913	$ 5,844	$ 8,184	[1],[2]	$ 3,202	[3]	$ 8,184	[1],[2]	$ 8,184	[1],[2]	$ 3,202	[3]	$ 3,383	[1],[2],[3]	$ 3,134		$ 3,041
Allowance for credit losses, period increase (decrease)			$ 1,300				$ 4,800		$ 2,300
Expected Future Unemployment Rate			16.00%				16.00%		16.00%
Expected Future Unemployment Rate Recovery			11.00%				11.00%		11.00%
Expected Future Decline in GDP			30.00%				30.00%		30.00%
ExpectedAnnualFutureDeclineInGDP			10.00%				10.00%		10.00%
Reasonable and supportable forecast period		18 months
Reversion period	12 months	12 months
Private student loans in repayment			$ 5,600				$ 5,600		$ 5,600				5,600
Private student loans in forbearance			$ 21				$ 21		21				46
Percentage of defaulted loans that were charged off at the end of the month in which they defaulted (in percent)			61.00%		39.00%		48.00%				39.00%
Personal Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maximum period of payment reduction for the temporary reduced payment program (in months)							12 months
Maximum repayment term for temporary modification programs (in years)							9 years
Maximum repayment term for permanent modification programs (in years)							9 years
Credit Card Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses	$ 5,306	$ 4,550	$ 6,491		$ 2,691	[3]	$ 6,491		$ 6,491		$ 2,691	[3]	$ 2,883	[3]	$ 2,622		$ 2,528
Maximum period of payment reduction for the temporary reduced payment program (in months)							12 months
Permanent workout program maturity (in months)							60 months
Interest and fees forgiven due to credit card loan modification program			$ 18		$ 17		$ 39				$ 34
Accounting Standards Update 2016-13 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for credit losses		2,500
Allowance for credit losses, period increase (decrease)		$ 2,500

[1] Prior to adoption of Accounting Standards Update ("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.