Fair Value - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013 reporting_unit	Dec. 31, 2012
Fair Value Disclosures [Abstract]
Fixed rate debt carrying value	$ 830	$ 1,030
Fixed rate debt difference between carrying value and fair value	$ 6	$ 46
Number of reporting units	10