Loan Receivables (Narrative) (Details) $ in Millions				3 Months Ended
	Mar. 31, 2020 USD ($)		Jan. 01, 2020 USD ($)	Mar. 31, 2020 USD ($)		Mar. 31, 2020 USD ($) segment		Mar. 31, 2019 USD ($)		Dec. 31, 2019 USD ($)		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	[1],[2]	$ 5,844	$ 6,913	[1],[2]	$ 6,913	[1],[2]	$ 3,134	[3]	$ 3,383	[1],[2],[3]	$ 3,041
Allowance for credit losses, period increase (decrease)				$ 1,100		$ 3,500
Expected future unemployment rate	9.00%			9.00%		9.00%
Expected future decline in GDP	18.00%			18.00%		18.00%
Reasonable and supportable forecast period	12 months		18 months
Reversion period	12 months		12 months
Private student loans in repayment	$ 5,500			$ 5,500		$ 5,500				5,600
Private student loans in forbearance	61			61		$ 61				46
Percentage of defaulted loans that were charged off at the end of the month in which they defaulted (in percent)						40.00%		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	$ 5,306		$ 5,306		$ 2,622	[3]	$ 2,883	[3]	$ 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						$ 21		$ 17
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.