Goodwill, Customer Relationships and Other Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Finite-Lived Intangible Assets [Line Items]
Other intangible assets, net	$ 1,555	$ 1,647
Goodwill	20,742	20,755	$ 20,674
Indefinite-life intangible assets	269	268
Amortization expense for intangible assets	1,353	1,470	$ 1,589
Gross carrying amount of intangible assets	33,671
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Finite lived intangible assets, net	3,928	4,893
Accumulated amortization	5,648	4,683
Capitalized software
Finite-Lived Intangible Assets [Line Items]
Finite lived intangible assets, net	1,248	1,338
Accumulated amortization	1,778	1,533
Tradenames and patents
Finite-Lived Intangible Assets [Line Items]
Finite lived intangible assets, net	38	41
Accumulated amortization	$ 20	$ 196