Combined Summarized Operating Results for Affiliates (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Investments In And Advances To Affiliates Schedule Of Investments [Abstract]
Total revenues	$ 599	$ 769	$ 810
Expenses	(437)	(558)	(577)
Depreciation and amortization	(73)	(84)	(99)
Operating profit	89	127	134
Interest income	5	3
Interest expense	(57)	(80)	(86)
Gain (loss) on dispositions	(2)	141	12
Net income	$ 35	$ 191	$ 60