Other Current Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Assets [Abstract]
Unrealized gains on derivative contracts	$ 449	$ 624
Deferred receivables consideration	307	540
Customer Omnibus Receivable	477	521
Financing Receivable, Net	413	373
Premiums Receivable, Net	129	648
Prepaid Expense, Current	232	268
Tax receivables	425	480
Other Receivables	371	478
Other current assets	372	451
Total other current assets	3,175	4,383
Financing Receivable, Allowance for Credit Losses	6	7
Interest on financing receivables	25	22	$ 23
Reinsurance Recoverables	$ 91	$ 223