Stock-Based Compensation, Dividend Restrictions, and Calculations of Earnings Per Share of Common Stock - Calculation of Earnings Per Share of Common Stock (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Net Income from Continuing Operations	$ 121	$ 91	$ 53	$ 53					$ 318	$ 242	$ 110
Net income (loss) from discontinued operations	9								9		(322)
Net Income (Loss)	$ 130	$ 91	$ 53	$ 53	$ 35	$ 79	$ 53	$ 75	$ 327	$ 242	$ (212)
Average shares outstanding									253	251	246
Adjustment to shares outstanding									0	0	0
Weighted Average Shares Outstanding for Computation of Basic Earnings Per Share of Common Stock									253	251	246
Net effect of potentially dilutive shares									1	1
Weighted Average Shares Outstanding for Computation of Diluted Earnings Per Share of Common Stock									254	252	246
Basic earnings per share of common stock from continuing operations									$ 1.25	$ 0.96	$ 0.45
Basic earnings (loss) per share of common stock from discontinued operations									0.04		(1.31)
Basic earnings (loss) per share									1.29	0.96	(0.86)
Diluted earnings per share of common stock from continuing operations									1.25	0.96	0.45
Diluted earnings (loss) per share of common stock from discontinued operations									0.04		(1.31)
Diluted earnings (loss) per share									$ 1.29	$ 0.96	$ (0.86)