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, 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 (loss) for basic EPS									$ 313	$ 245	$ 16
Convertible debt interest, net of tax									0	1	0
Net income (loss) for diluted EPS									$ 313	$ 246	$ 16
Basic weighted average shares outstanding	99.5	102.7	105.5	106.1	106.2	103.9	105.1	106.6	103.4	105.4	107.6
Options, warrants and non-vested stock									1.6	2.1	3.8
Convertible debt									0.0	3.1	0.0
Diluted weighted average shares outstanding	99.5	104.0	106.7	106.1	108.3	109.9	111.0	108.6	105.0	110.6	111.4
Earnings (loss) per share:
Basic (in dollars per share)	$ (0.06)	$ 1.80	$ 1.36	$ (0.09)	$ 0.22	$ 1.84	$ 0.25	$ 0.03	$ 3.02	$ 2.32	$ 0.15
Diluted (in dollars per share)	$ (0.06)	$ 1.77	$ 1.34	$ (0.09)	$ 0.21	$ 1.74	$ 0.24	$ 0.03	$ 2.98	$ 2.22	$ 0.15