Subsequent Events - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Feb. 29, 2016	Dec. 31, 2015
Subsequent Event
Subsequent Event [Line Items]
Net proceeds from issuance of common stock and Mandatory convertible preferred stock, after deducting underwriting discounts, commissions, and estimated offering expenses	$ 1,600,000,000
Subsequent Event | Minimum
Subsequent Event [Line Items]
Number of shares issued for each share of convertible preferred stock that is converted	21.822
Subsequent Event | Maximum
Subsequent Event [Line Items]
Number of shares issued for each share of convertible preferred stock that is converted	25.642
Subsequent Event | Final Average Price, $45.83 or less
Subsequent Event [Line Items]
Value of capped call transaction	$ 0
Subsequent Event | Final Average Price, $53.625 or higher
Subsequent Event [Line Items]
Value of capped call transaction	$ 98,000,000
Subsequent Event | Final Average Price between $45.83 and $53.625
Subsequent Event [Line Items]
Number of shares multiplied by difference between the Final Average Price	12,550,000
Subsequent Event | Common Stock
Subsequent Event [Line Items]
Shares of stock issued	28,750,000
Subsequent Event | Series A Mandatory Convertible Preferred Stock
Subsequent Event [Line Items]
Shares of stock issued	575,000
Preferred stock, dividend rate, percentage	8.00%
Preferred stock, par value	$ 1
Preferred stock, liquidation preference per share	$ 1,000
HOVENSA
Subsequent Event [Line Items]
Difference between estimated plan obligation and fair value of the asset plan		$ 30,000,000