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Cash Dividends - Additional Information (Detail) (USD $)
In Millions, except Per Share data, unless otherwise specified
3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Feb. 20, 2013
Statement Of Partners Capital [Abstract]      
Dividends Payable, Amount Per Share     $ 0.13
Aggregated Cash Dividends Paid $ 56 $ 51