Interest Expense for Debentures (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Debt Instrument [Line Items]
Non-cash interest expense due to discount amortization	$ 25		$ 13		$ 30
Total interest expense	304	[1]	373	[1]	371	[1]
Exchangeable Senior Debentures
Debt Instrument [Line Items]
Contractual interest expense (cash)	10		19		31
Non-cash interest expense due to discount amortization	15		17		31
Total interest expense	$ 25		$ 36		$ 62

[1] Interest expense and interest paid for 2013, 2012 and 2011 includes cash prepayment premiums of approximately $23 million, $21 million and $5 million, respectively.