Notes Receivable - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Receivables [Abstract]
Notes receivable past due	$ 0		$ 0
Unamortized discounts for notes receivable	29,000,000		29,000,000		$ 31,000,000
Investment in impaired notes receivables	74,000,000		74,000,000		72,000,000
Allowance for credit losses	57,000,000		57,000,000		55,000,000
Exposure to investment in impaired loans	17,000,000		17,000,000		$ 17,000,000
Average investment in impaired notes receivables	$ 73,000,000	$ 69,000,000	$ 73,000,000	$ 67,000,000