Income Taxes (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Effective tax rate of income (loss) before income taxes	35.70%	33.70%	34.90%	35.50%
Reduction in income tax expense	$ 1		$ 35
Equity in net losses of unconsolidated entities	8	$ 9	53	$ 32
Investments Qualifying for Federal Tax Credits [Member]
Equity in net losses of unconsolidated entities	6	7	21	22
Income tax (expense) benefit, including tax credits, from equity method investment	$ 14	$ 15	$ 39	$ 40