Investments (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Schedule of Trading Securities and Other Trading Assets [Line Items]
Investments	$ 268	$ 179
Investments in equity affiliates
Schedule of Trading Securities and Other Trading Assets [Line Items]
Investments	135	46
Other
Schedule of Trading Securities and Other Trading Assets [Line Items]
Investments	54	55
Trading Securities [Member] | Marketable equity securities - Trading (See Note 9)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Investments	$ 79	$ 78