Earnings per Share - Computation of Basic and Diluted Earnings per Share (EPS) (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Debt instrument, stated interest rate percentage		7.25%
Increase in net income for purposes of computing diluted earnings per share	$ 0	$ 5
Convertible Senior Notes, 7.25, Due in 2014 [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Debt instrument, stated interest rate percentage		7.25%