Accumulated Other Comprehensive Income - Other Comprehensive Income (Loss) Before Reclassifications Associated With Cash Flow Derivative Instruments (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) on derivatives before tax	$ (10)	$ 26	$ (18)	$ 25
Tax (expense) benefit	4	(10)	7	(10)
Net of tax	(6)	16	(11)	15
Interest Rate Swaps [Member] | Cash Flow Hedging [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) on derivatives before tax	0	10	(8)	12
Foreign Currency Derivatives [Member] | Cash Flow Hedging [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) on derivatives before tax	(12)	12	(2)	19
Electricity commodity derivatives [Member] | Cash Flow Hedging [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss) on derivatives before tax	$ 2	$ 4	$ (8)	$ (6)