Customer Deposits (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
U.S.:
Interest-bearing	$ 63,666	$ 52,316
Non-interest-bearing	395	367
Non-U.S.:
Interest-bearing	34	58
Non-interest-bearing	357	301
Total customer deposits	64,452	53,042
Card Member Credit Balances [Member]
U.S.:
Non-interest-bearing	358	331
Non-U.S.:
Non-interest-bearing	$ 344	$ 285