Other Liabilities - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Other Liabilities [Line Items]
Deferred gains on sale of assets included in accrued expenses and other liabilities	$ 1,341		$ 1,341		$ 1,168
Amortization of deferred gains	22	$ 22	44	$ 43
Accrued expenses	1,324		1,324		1,307
SPG [Member]
Other Liabilities [Line Items]
Total actuarial liability	1,120		1,120		1,115
Accrued expenses	$ 451		$ 451		$ 453