Segment Information - Depreciation Expense, by Segment (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reconciliation Of Depreciation By Segment [Line Items]
Depreciation expense	$ 3,616	$ 2,460	$ 1,653
North America
Reconciliation Of Depreciation By Segment [Line Items]
Depreciation expense	2,701	1,863	1,229
International
Reconciliation Of Depreciation By Segment [Line Items]
Depreciation expense	$ 915	$ 597	$ 424