Customer Deposits (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
U.S.:
Interest-bearing	$ 82,865	$ 72,445
Non-interest-bearing	1,101	415
Non-U.S.:
Interest-bearing	21	23
Non-interest-bearing	818	404
Total customer deposits	84,805	73,287
Card Member Credit Balances [Member]
U.S.:
Non-interest-bearing	1,076	389
Non-U.S.:
Non-interest-bearing	$ 816	$ 401