Customer Deposits (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
U.S.:
Interest-bearing	$ 72,535	$ 69,144
Non-interest-bearing	358	412
Non-U.S.:
Interest-bearing	22	28
Non-interest-bearing	383	376
Total customer deposits	73,298	69,960
Card Member Credit Balances [Member]
U.S.:
Non-interest-bearing	329	376
Non-U.S.:
Non-interest-bearing	$ 376	$ 367