Derivatives - Classification of Gross Fair Values of Derivative Instruments, Excluding Cash Collateral (Detail) (Commodity derivatives, Other current assets, USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Commodity derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Asset	$ 44	$ 21
Liability	$ 91	$ 53