Segment Information - Schedule of consolidated non-current assets by geographic area (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 13,805	$ 13,728
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	7,793	7,720
Europe, Middle East and Africa [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	2,179	2,440
Americas other than U.S. [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	493	559
United Kingdom [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	2,700	2,392
Asia Pacific [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 640	$ 617