Summary of Significant Accounting Policies - Activity in Redeemable Capital Shares (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2013
Temporary Equity [Line Items]
Redeemable capital shares, prescribed aggregation	50,000	50,000
Period for Share settlement, days		3 days
Beginning balance, Shares	701,600,000	719,550,000
Shares issued, Shares		42,750,000
Shares redeemed, Shares	(109,150,000)	(169,850,000)
Ending balance, Shares	592,450,000	592,450,000
Beginning balance, Amount	$ 10,899,390	$ 11,645,298
Shares issued, Amount		672,521
Shares redeemed, Amount	(1,483,453)	(2,425,068)
Redemption value adjustment, Amount	(2,556,187)	(3,033,001)
Ending balance, Amount	$ 6,859,750	$ 6,859,750