Customer Deposits (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
U.S.:
Interest-bearing	$ 72,110	$ 69,144
Non-interest-bearing	368	412
Non-U.S.:
Interest-bearing	27	28
Non-interest-bearing	352	376
Total customer deposits	72,857	69,960
Card Member Credit Balances [Member]
U.S.:
Non-interest-bearing	334	376
Non-U.S.:
Non-interest-bearing	$ 343	$ 367