Segment Information - Total Assets Fixed Assets Net and Total Fixed Asset Additions By Segment (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 54,505	$ 40,159
Property and equipment, net	16,967	10,949
Total property and equipment additions	9,481	6,373
North America
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	39,157	26,108
Property and equipment, net	13,163	8,447
Total property and equipment additions	7,464	4,837
International
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	15,348	14,051
Property and equipment, net	3,804	2,502
Total property and equipment additions	$ 2,017	$ 1,536