Business Segments - Segment Assets (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Total assets	$ 16,511	$ 16,391	$ 18,000
Operating Segments
Segment Reporting Information [Line Items]
Total assets	13,601	13,211	14,567
Operating Segments | Americas
Segment Reporting Information [Line Items]
Total assets	6,701	6,275	7,019
Operating Segments | Europe, Middle East and Africa
Segment Reporting Information [Line Items]
Total assets	4,385	4,377	4,954
Operating Segments | Asia Pacific
Segment Reporting Information [Line Items]
Total assets	2,515	2,559	2,594
Corporate
Segment Reporting Information [Line Items]
Total assets	$ 2,910	$ 3,180	$ 3,433