Derivative Instruments and Hedging Activities - Impact of Pretax Income on Cash Flow Derivatives on Comprehensive Income and Results of Operations (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain (Loss) Recognized in OCI (Effective Portion)	$ (36)	$ (50)	$ (71)
Derivative Gain (Loss) Reclassified from AOCI into Income (Effective Portion)	(15)	(2)	(30)
Forward Starting Interest Rate Swaps [Member] | Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain (Loss) Recognized in OCI (Effective Portion)	(27)	(59)	(33)
Derivative Gain (Loss) Reclassified from AOCI into Income (Effective Portion)	(3)	(1)
Treasury Rate Locks [Member] | Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain (Loss) Recognized in OCI (Effective Portion)			(11)
Derivative Gain (Loss) Reclassified from AOCI into Income (Effective Portion)	(7)	(7)	(8)
Foreign Currency Derivatives [Member] | Other Income (Expense) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain (Loss) Recognized in OCI (Effective Portion)	(9)	1	(22)
Derivative Gain (Loss) Reclassified from AOCI into Income (Effective Portion)	(15)	4	(18)
Electric Derivative [Member] | Operating Revenues (Expense) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain (Loss) Recognized in OCI (Effective Portion)		8	(5)
Derivative Gain (Loss) Reclassified from AOCI into Income (Effective Portion)	$ 10	$ 2	$ (4)