Financial Risk Management - Gross Volumes of Corporation's Derivative Contracts Outstanding (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Interest rate swap [Member]
Derivative [Line Items]
Derivative notional amount	$ 1,300,000,000	$ 1,300,000,000
Gross Volumes of the Financial Risk Management Derivative Contracts Outstanding [Member] | Foreign Exchange [Member]
Derivative [Line Items]
Derivative notional amount	862,000,000	1,189,000,000
Gross Volumes of the Financial Risk Management Derivative Contracts Outstanding [Member] | Interest rate swap [Member]
Derivative [Line Items]
Derivative notional amount	$ 1,300,000,000	$ 1,300,000,000
Gross Volumes of the Financial Risk Management Derivative Contracts Outstanding [Member] | Commodity, Primarily Crude Oil (Millions of Barrels) [Member]
Derivative [Line Items]
Absolute volume of derivative commodity contracts	16