Financial Instruments - Disclosure of Outstanding Forward Agreements to Purchase Foreign Currency (Detail) - Less than 1 year [member] - Forward agreements to purchase foreign currency [member] - MXN ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Disclosure of Financial Assets and Financial Liabilities [Line Items]
Notional amount	$ 7,739	$ 8,265
Fair Value Liability	(20)	(247)
Fair Value Asset	$ 172	$ 364

Financial Instruments - Disclosure of Outstanding Forward Agreements to Purchase Foreign Currency (Detail) - Less than 1 year [member] - Forward agreements to purchase foreign currency [member] - MXN ($)
$ in Millions

Dec. 31, 2017

Dec. 31, 2016

Disclosure of Financial Assets and Financial Liabilities [Line Items]

Notional amount

$ 7,739

$ 8,265

Fair Value Liability

(20)

(247)

Fair Value Asset

$ 172

$ 364