Effect of Changes in Fair Value Related to Derivative Instruments on Consolidated Statements of Income (Detail) (Not Designated as Hedging Instrument [Member], USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012
Derivative [Line Items]
Effect on income of derivative instruments not designated as hedging instruments	$ 1	$ 2	$ 1
Note Hedge [Member] | Noncash convertible debt related expense [Member]
Derivative [Line Items]
Effect on income of derivative instruments not designated as hedging instruments	57	(65)	(11)
Cash Conversion Option [Member] | Noncash convertible debt related expense [Member]
Derivative [Line Items]
Effect on income of derivative instruments not designated as hedging instruments	(56)	67	12
Contingent interest features of the 3.25% Notes and Debentures [Member] | Noncash convertible debt related expense [Member]
Derivative [Line Items]
Effect on income of derivative instruments not designated as hedging instruments	$ 0	$ 0	$ 0