Segments and Geographic Information Segment and Geographic Information ( Revenue by Segment) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues	$ 2,643	$ 2,693	$ 2,613	$ 2,581	$ 2,660	$ 2,639	$ 2,452	$ 2,530	$ 10,530	$ 10,281	$ 11,260
Corporate, Non-Segment [Member] | Corporate and Other
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									35	77	31
Intersegment Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									(24)	(23)	(43)
Operating Segments [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									10,530	10,281	11,260
Operating Segments [Member] | UNITED STATES
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									3,229	3,429	3,593
Operating Segments [Member] | ANDES [Domain]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									2,710	2,506	2,489
Operating Segments [Member] | Brazil
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									542	450	962
Operating Segments [Member] | MCAC [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									2,448	2,172	2,353
Operating Segments [Member] | EURASIA [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenues									$ 1,590	$ 1,670	$ 1,875