Partnership Capital Subject to Mandatory Redemption - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Jan. 02, 2015	Jan. 17, 2014	Dec. 31, 2012
Partners Capital Account [Line Items]
Period of loans made by Partnership to general partners	1 year
Outstanding amount of partner loans financed through the Partnership	$ 218	$ 198	$ 215			$ 170
Interest income from outstanding amount of general partner loan	$ 8	$ 7	$ 8
Limited Partnership's minimum annual return rate	7.50%	7.50%	7.50%
Limited partnership's minimum return, value	$ 69	$ 48	$ 48
2014 Limited Partnership Offering [Member]
Partners Capital Account [Line Items]
Limited partnership amount registered					$ 350
Limited partnership interests issued				$ 292
Remaining limited partnership interests that may be issued	$ 58