Inventory (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Inventory Disclosure [Abstract]
Raw materials	$ 1,103	$ 955
Work-in-process	323	428
Finished goods	1,226	1,115
Inventory at FIFO	2,652	2,498
Excess of FIFO over LIFO cost	(120)	(116)
Total inventory	$ 2,532	$ 2,382