Stockholders' Equity - Additional Information (Detail) (USD $)	0 Months Ended	3 Months Ended	12 Months Ended
	Jan. 21, 2015	Mar. 31, 2015	Dec. 31, 2014
Stockholders Equity Note [Line Items]
Preferred stock, shares authorized		10,000,000	10,000,000
Preferred stock, without par value		$ 0	$ 0
Preferred stock		$ 388,500,000	$ 388,500,000
Stock repurchase, shares		1,600,000
Average price paid per share for common stock repurchased		$ 68.93
Stock repurchase, aggregate cost		107,200,000
Upper Limit
Stockholders Equity Note [Line Items]
Stock repurchase authorized value		15,000,000
Between April 2015 and June 2016 | Upper Limit
Stockholders Equity Note [Line Items]
Stock Repurchase Authorized Amount		675,000,000
Series C Preferred Stock
Stockholders Equity Note [Line Items]
Stock issued during period		16,000,000	16,000,000
Per share ownership interest, percentage		0.10%	0.10%
Preferred stock, without par value		$ 0	$ 0
Preferred stock, liquidation preference		25,000	25,000
Depository shares, liquidation preference per share		$ 25	$ 25
Preferred stock		$ 388,500,000	$ 388,500,000
Preferred stock, annual dividend rate		5.85%
Preferred Stock, Dividends Per Share, Declared	$ 365.625
Dividends Payable, Date to be Paid	Apr. 01, 2015
Dividends Payable, Date of Record	Mar. 15, 2015