Income Taxes - Additional information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Taxes [Line Items]
Effective tax rate of income (loss) before income taxes	33.70%	32.30%	35.50%	27.80%
Equity in net losses of unconsolidated entities	$ 9	$ 9	$ 32	$ 32
Investments Qualifying for Federal Tax Credits [Member]
Income Taxes [Line Items]
Equity in net losses of unconsolidated entities	7	7	22	21
Income tax benefit, including tax credits, from equity method investment	15	17	40	41
Low-Income Housing Properties [Member]
Income Taxes [Line Items]
Interest expense	$ 1	$ 1	$ 2	$ 3