Combined Summarized Operating Results for Affiliates (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Investments In And Advances To Affiliates Schedule Of Investments [Abstract]
Total revenues	$ 728	$ 776	$ 617
Expenses	(545)	(568)	(489)
Depreciation and amortization	(75)	(91)	(131)
Operating profit (loss)	108	117	(3)
Interest income	3
Interest expense	(72)	(79)	(59)
Gain on disposition	141	12	2
Net income (loss)	$ 180	$ 50	$ (60)