Stock-Based Compensation (Stock Based Compensation Activity) (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2021	Sep. 30, 2020
Number of Shares
Balance (in shares)	692	692
Weighted Average Grant Date Fair Value
Cost not yet recognized	$ 36	$ 36
Period for recognition	1 year 3 months 18 days
Time-based RSUs
Number of Shares
Balance (in shares)		1,070
Granted (in shares)	240
Vested (in shares)	(575)
Canceled (in shares)	(43)
Outstanding and expected to vest (in shares)	692	692
Weighted Average Grant Date Fair Value
Balance (in dollars per share)		$ 27.47
Granted (in dollars per share)	$ 63.12		$ 23.14
Vested (in dollars per share)	29.46
Canceled (in dollars per share)	31.37
Balance (in dollars per share)	37.93	37.93
Outstanding and expected to vest, weighted average grant date fair value (in dollars per share)	$ 37.93	$ 37.93
Outstanding and expected to vest weighted average remaining contractual term (in years)	1 year 1 month 6 days
Aggregate intrinsic value, outstanding and expected to vest	$ 81	$ 81
Fair value vested in period		$ 17	$ 19
Performance-based and market-based RSUs
Number of Shares
Balance (in shares)		988
Granted (in shares)	236
Vested (in shares)	0
Canceled (in shares)	(324)
Balance (in shares)	900	900
Outstanding and expected to vest (in shares)	900	900
Weighted Average Grant Date Fair Value
Balance (in dollars per share)		$ 32.41
Granted (in dollars per share)	$ 62.27		$ 21.06
Vested (in dollars per share)	0
Canceled (in dollars per share)	45.92
Balance (in dollars per share)	35.37	35.37
Outstanding and expected to vest, weighted average grant date fair value (in dollars per share)	$ 35.37	$ 35.37
Outstanding and expected to vest weighted average remaining contractual term (in years)	1 year 6 months
Outstanding weighted average remaining contractual terms (in years)	1 year 6 months
Aggregate intrinsic value outstanding	$ 105	$ 105
Aggregate intrinsic value, outstanding and expected to vest	$ 105	$ 105