Summary of Significant Accounting Policies - Customer Rewards Reserve and Revenue Recognition (Details) - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Customer Reward Program	$ 3.2	$ 2.7
Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Partnership Agreement Initial Term	2 years
Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Partnership Agreement Initial Term	10 years
Credit Card Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan Commitment and Origination Fees and Discounts or Premiums, Amortization Period	12 months