Business Developments and Discontinued Operations - Business Developments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Payments to Acquire Businesses, Net of Cash Acquired	$ 3,187	$ 629	$ 9,314
Cabela [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Net of Cash Acquired	3,200
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	5,900
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Credit Card Receivables	5,700
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities	2,600
Business combination, recognized identifiable assets acquired and liabilities assumed, securitized debt obligation	$ 2,500