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Cash Dividends - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2015
Jun. 30, 2014
Jun. 30, 2015
Jun. 30, 2014
May. 13, 2015
Statement of Partners' Capital [Abstract]          
Dividends payable, amount per share         $ 0.46
Cash dividends paid $ 178 $ 198 $ 363 $ 309