Computation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Net income for basic EPS									$ 163	$ 313	$ 245
Convertible debt interest, net of tax									0	0	1
Net income for diluted EPS									$ 163	$ 313	$ 246
Basic weighted average shares outstanding	87.4	90.4	93.9	96.3	99.5	102.7	105.5	106.1	92.0	103.4	105.4
Options, warrants and non-vested stock									1.3	1.6	2.1
Convertible debt									0.0	0.0	3.1
Diluted weighted average shares outstanding	87.4	91.8	95.1	96.3	99.5	104.0	106.7	106.1	93.3	105.0	110.6
Earnings (loss) per share:
Basic	$ (0.35)	$ 2.32	$ 0.39	$ (0.53)	$ (0.06)	$ 1.80	$ 1.36	$ (0.09)	$ 1.78	$ 3.02	$ 2.32
Diluted	$ (0.35)	$ 2.28	$ 0.38	$ (0.53)	$ (0.06)	$ 1.77	$ 1.34	$ (0.09)	$ 1.75	$ 2.98	$ 2.22