Customer Deposits (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
U.S.:
Interest-bearing	$ 76,459	$ 72,445
Non-interest-bearing	815	415
Non-U.S.:
Interest-bearing	25	23
Non-interest-bearing	663	404
Total customer deposits	77,962	73,287
Card Member Credit Balances [Member]
U.S.:
Non-interest-bearing	791	389
Non-U.S.:
Non-interest-bearing	$ 661	$ 401