Earning Per Share - Additional Information (Detail) - Entity [Domain] - USD ($) shares in Millions	1 Months Ended	3 Months Ended	6 Months Ended
	Jan. 31, 2015	Jun. 30, 2015	Jun. 30, 2015	Jul. 21, 2015	Dec. 31, 2014
Earnings Loss Per Share [Line Items]
Share repurchase program authorized amount					$ 1,000,000,000
Payments for repurchases of common stock			$ 445,000,000
Share repurchase program remaining authorized amount		$ 230,000,000	$ 230,000,000
Share repurchase program completion date			Dec. 31, 2017
Open Market Repurchases
Earnings Loss Per Share [Line Items]
Payments for repurchases of common stock		$ 250,000,000	$ 450,000,000
Number of shares repurchased		4.4	7.3
Subsequent Event
Earnings Loss Per Share [Line Items]
Share repurchase program authorized amount				$ 3,000,000,000
Unsecured Debt | 4.5% Convertible Notes Due 2015
Earnings Loss Per Share [Line Items]
Long-term Debt, Gross	$ 202,000,000	$ 202,000,000	$ 202,000,000
Debt instrument stated interest rate	4.50%	4.50%	4.50%
Common stock issued in exchange for convertible notes	11.0		11.0
Debt instrument maturity year	2015
Convertible debt outstanding		$ 0	$ 0