Customer Deposits (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
U.S.:
Interest-bearing	$ 83,963	$ 72,445
Non-interest-bearing	726	415
Non-U.S.:
Interest-bearing	20	23
Non-interest-bearing	752	404
Total customer deposits	85,461	73,287
Card Member Credit Balances [Member]
U.S.:
Non-interest-bearing	701	389
Non-U.S.:
Non-interest-bearing	$ 749	$ 401