Schedule Of Selected Quarterly Financial Data (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
Quarterly Financial Information Disclosure [Abstract]
Net revenues	$ 1,879	$ 2,656	$ 2,243	$ 1,881	$ 1,902	$ 2,577	$ 2,173	$ 1,850
Net income (loss)	$ (31)	$ 209	$ 36	$ (51)	$ (5)	$ 184	$ 143	$ (9)
Basic Net income (loss) (in dollars per share)	$ (0.35)	$ 2.32	$ 0.39	$ (0.53)	$ (0.06)	$ 1.80	$ 1.36	$ (0.09)	$ 1.78	$ 3.02	$ 2.32
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
Diluted Net income (loss) (in dollars per share)	$ (0.35)	$ 2.28	$ 0.38	$ (0.53)	$ (0.06)	$ 1.77	$ 1.34	$ (0.09)	$ 1.75	$ 2.98	$ 2.22
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