Provision for Income Taxes Provision for Income Taxes (Reconciliation of Amounts of Unrecognized Tax Benefits) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Total unrecognized tax benefits as of January 1	$ 901	$ 805	$ 800
Gross amounts of decreases in unrecognized tax benefits as a result of tax positions taken during the prior period	(50)	(28)	(94)
Gross amounts of increases in unrecognized tax benefits as a result of tax positions taken during the prior period	84	76	73
Gross amounts of increases in unrecognized tax benefits as a result of tax positions taken during the current period	92	92	78
Amount of decreases in the unrecognized tax benefits relating to settlements	(15)	(19)	(29)
Reduction to unrecognized tax benefits as a result of a lapse of the applicable statute of limitations	(3)	(6)	(10)
Exchange gain	(23)	(19)	(13)
Total unrecognized tax benefits as of December 31	986	901	805
Total unrecognized tax benefits that, if recognized, would impact the effective tax rate	818	778	693
Total amount of interest and penalties recognized in the Consolidated Income Statements	5	16	4
Total amount of interest and penalties recognized in the Consolidated Balance Sheets	$ 117	$ 122	$ 116