Loan Receivables and Allowance for Loan Losses - Allowance for Loan Losses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	$ 3,497	$ 3,236	$ 2,892
Provision charged to operations	3,986	2,952	2,917
Gross charge-offs	(3,969)	(3,371)	(3,189)
Recoveries	830	680	616
Ending Balance	4,344	3,497	3,236
Credit cards
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	3,420	3,169	2,827
Provision charged to operations	3,898	2,880	2,858
Gross charge-offs	(3,873)	(3,289)	(3,111)
Recoveries	809	660	595
Ending Balance	4,254	3,420	3,169
Consumer installment loans
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	26	22	19
Provision charged to operations	43	25	20
Gross charge-offs	(45)	(35)	(30)
Recoveries	13	14	13
Ending Balance	37	26	22
Commercial credit products
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	50	45	46
Provision charged to operations	45	46	39
Gross charge-offs	(51)	(47)	(48)
Recoveries	8	6	8
Ending Balance	52	50	45
Other
Allowance for Loan and Lease Losses [Roll Forward]
Beginning Balance	1	0
Provision charged to operations	0	1
Gross charge-offs	0	0
Recoveries	0	0
Ending Balance	$ 1	$ 1	$ 0