Capital Stock - Summary of Amounts Recognized as Expense and Capitalized Cost for Each Plan (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Summary of amounts recognized as expense and capitalized cost
Compensation expense	$ 167	$ 113	$ 164
Capitalized costs	67	42	71
Share Appreciation Program 2008 [Member]
Summary of amounts recognized as expense and capitalized cost
Compensation expense	22	8	49
Compensation expense, net of tax	14	5	31
Capitalized costs	12	5	27
Share Appreciation Plan 2005 [Member]
Summary of amounts recognized as expense and capitalized cost
Compensation expense		1	6
Compensation expense, net of tax		1	4
Capitalized costs		$ 1	$ 3