Customer Deposits (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
U.S.:
Interest-bearing	$ 88,088	$ 85,583
Non-interest-bearing (includes Card Member credit balances of: 2021, $461; 2020, $576)	483	599
Non-U.S.:
Interest-bearing	19	19
Non-interest-bearing (includes Card Member credit balances of: 2021, $600; 2020, $671)	603	674
Total customer deposits	89,193	86,875
Card Member Credit Balances
U.S.:
Non-interest-bearing (includes Card Member credit balances of: 2021, $461; 2020, $576)	461	576
Non-U.S.:
Non-interest-bearing (includes Card Member credit balances of: 2021, $600; 2020, $671)	$ 600	$ 671