Debt (Schedule of Notes Payable and Long-Term Debt) (Parenthetical) (Detail) (USD $)	9 Months Ended
	Oct. 31, 2014
Notes Which Mature In December 2020
Debt Instrument [Line Items]
Senior unsecured notes, face amount	$ 450,000,000
Debt maturity date	Dec. 01, 2020
Notes Which Mature In December 2040
Debt Instrument [Line Items]
Senior unsecured notes, face amount	300,000,000
Debt maturity date	Dec. 01, 2040
Notes Which Mature In July 2032
Debt Instrument [Line Items]
Senior unsecured notes, face amount	250,000,000
Debt maturity date	Jul. 01, 2032
Notes Which Mature In July 2033
Debt Instrument [Line Items]
Senior unsecured notes, face amount	$ 300,000,000
Debt maturity date	Jul. 01, 2033