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Notes Receivable - Additional Information (Detail) (USD $)
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3 Months Ended | ||
|---|---|---|---|
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Mar. 31, 2015
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Mar. 31, 2014
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Dec. 31, 2014
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| Receivables [Abstract] | |||
| Notes receivable, past due | $ 0 | ||
| Notes receivable, unamortized discounts, balance | 25,000,000 | 25,000,000 | |
| Notes receivable reserve representing an allowance for credit losses | 50,000,000 | 50,000,000 | |
| Investment in impaired notes receivables | 66,000,000 | 63,000,000 | |
| Investment in impaired loans with no related allowance for credit losses | 16,000,000 | 13,000,000 | |
| Average investment in notes receivables | $ 65,000,000 | $ 101,000,000 | |