Summary of Significant Accounting Policies - Recently Issued and Adopted Accounting Standards (Details) - USD ($) $ in Millions		Jan. 01, 2020	Dec. 31, 2020	Dec. 31, 2019		Dec. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Shareholders' equity			$ (22,984)	$ (23,071)		$ (22,290)	$ (18,261)
Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Shareholders' equity			(13,837)	(13,871)		(12,499)	(8,307)
Card Member Receivables [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Receivable reserves			$ (267)	(619)		$ (573)	$ (521)
Cumulative Effect, Period of Adoption, Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Current and deferred tax impact		$ 288
Shareholders' equity	[1]			882
Cumulative Effect, Period of Adoption, Adjustment [Member] | Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Shareholders' equity		882		882	[1]
Cumulative Effect, Period of Adoption, Adjustment [Member] | Total Loans [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in financing receivable, allowance		1,663
Cumulative Effect, Period of Adoption, Adjustment [Member] | Card Member Receivables [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in financing receivable, allowance		(493)
Receivable reserves		$ 493		$ (126)

[1] Represents $1,170 million, net of tax of $288 million, related to the impact as of January 1, 2020 of adopting the new accounting guidance for the recognition of credit losses on certain financial instruments.