Revision of Previously Issued Financial Statements - Schedule of Impact on Company's Previously Issued Unaudited Consolidated Balance Sheets and Statements of Cash Flows (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended				3 Months Ended		6 Months Ended		9 Months Ended	12 Months Ended			3 Months Ended		6 Months Ended		9 Months Ended	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Dec. 31, 2011	Mar. 31, 2013 Scenario, Previously Reported [Member]	Mar. 31, 2012 Scenario, Previously Reported [Member]	Jun. 30, 2013 Scenario, Previously Reported [Member]	Jun. 30, 2012 Scenario, Previously Reported [Member]	Sep. 30, 2012 Scenario, Previously Reported [Member]	Dec. 31, 2012 Scenario, Previously Reported [Member]	Dec. 31, 2011 Scenario, Previously Reported [Member]	Dec. 31, 2010 Scenario, Previously Reported [Member]	Mar. 31, 2013 Restatement Adjustment [Member]	Mar. 31, 2012 Restatement Adjustment [Member]	Jun. 30, 2013 Restatement Adjustment [Member]	Jun. 30, 2012 Restatement Adjustment [Member]	Sep. 30, 2012 Restatement Adjustment [Member]	Dec. 31, 2012 Restatement Adjustment [Member]	Dec. 31, 2011 Restatement Adjustment [Member]	Dec. 31, 2010 Restatement Adjustment [Member]
Cash and cash investments	$ 1,011	$ 889	$ 1,040	$ 1,353	$ 1,032	$ 1,788	$ 1,223	$ 1,853	$ 1,166	$ 1,351	$ 1,656		$ 828	$ 1,491	$ 1,028	$ 1,612	$ 889	$ 1,040	$ 1,353
Short-term bank deposits													204	297	195	241	277
Net cash (for) from investing activities	$ (21)	$ (17)			$ (30)	$ (2)	$ (51)	$ (15)	$ (42)	$ (27)	$ (61)	$ (109)	$ 70	$ 10	$ 62	$ 37	$ (17)	$ (29)	$ (84)	$ (244)