Customer Deposits (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
U.S.:
Interest-bearing	$ 57,012	$ 52,316
Non-interest-bearing	348	367
Non-U.S.:
Interest-bearing	29	58
Non-interest-bearing	337	301
Total customer deposits	57,726	53,042
Card Member Credit Balances [Member]
U.S.:
Non-interest-bearing	309	331
Non-U.S.:
Non-interest-bearing	$ 325	$ 285