Customer Deposits (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
U.S.:
Interest-bearing	$ 71,808	$ 69,144
Non-interest-bearing	386	412
Non-U.S.:
Interest-bearing	27	28
Non-interest-bearing	369	376
Total customer deposits	72,590	69,960
Card Member Credit Balances [Member]
U.S.:
Non-interest-bearing	351	376
Non-U.S.:
Non-interest-bearing	$ 362	$ 367