Customer Deposits (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
U.S.:
Interest-bearing	$ 69,144	$ 63,666
Non-interest-bearing	412	395
Non-U.S.:
Interest-bearing	28	34
Non-interest-bearing	376	357
Total customer deposits	69,960	64,452
Card Member Credit Balances [Member]
U.S.:
Non-interest-bearing	376	358
Non-U.S.:
Non-interest-bearing	$ 367	$ 344