Customer Deposits (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
U.S.:
Interest-bearing	$ 85,583	$ 72,445
Non-interest-bearing	599	415
Non-U.S.:
Interest-bearing	19	23
Non-interest-bearing	674	404
Total customer deposits	86,875	73,287
Card Member Credit Balances [Member]
U.S.:
Non-interest-bearing	576	389
Non-U.S.:
Non-interest-bearing	$ 671	$ 401