Partnership Capital Subject to Mandatory Redemption - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 02, 2020	Jan. 02, 2019	Jan. 12, 2018	Dec. 31, 2016
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	$ 360	$ 332	$ 297				$ 266
Interest income from outstanding amount of general partner loan	$ 21	$ 17	$ 13
Limited partnership's minimum annual return rate	7.50%	7.50%	7.50%
Limited partnership's minimum return, value	$ 94	$ 67	$ 67
2018 Limited Partnership Offering [Member]
Partners Capital Account [Line Items]
Limited partnership amount registered						$ 450
Limited partnership interests issued				$ 1	$ 380
Remaining limited partnership interests that may be issued	$ 69