Derivative Instruments and Hedging Activities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Issued notes	$ 400
Forecasted debt issuance variable rate period	3-month LIBOR
Ineffective portion of the cash flow hedges	2
Loss from the termination of the interest rate swap agreement	22		23
Percentage of interest rate swap effectiveness			100.00%
Interest rate swap recorded in other comprehensive income	23
Decrease in interest expense due to amortization of net gains on termination of interest rate swap agreement	4	8
Additional expense related to the cash flow hedge terminated	$ 1