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	12 Months Ended
	Jun. 30, 2012	Jun. 30, 2012	Dec. 31, 2011
Temporary Equity [Line Items]
Redeemable capital shares, prescribed aggregation	50,000	50,000
Period for Share settlement, days		3 days
Beginning balance, Shares	596,450,000	563,850,000
Shares issued, Shares	23,700,000	61,400,000
Shares redeemed, Shares	(22,700,000)	(27,800,000)
Ending balance, Shares	597,450,000	597,450,000	563,850,000
Beginning balance, Amount	$ 9,662,321	$ 8,416,801
Shares issued, Amount	368,304	998,830
Shares redeemed, Amount	(348,173)	(430,539)
Redemption value adjustment, Amount	(382,245)	(315,115)	(356,503)
Ending balance, Amount	$ 9,300,207	$ 9,300,207	$ 8,416,801