DEBT - Additional Information (Detail) (USD $)	Mar. 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Guaranteed loan, loan balance	$ 5,200,000
$1 billion revolver weighted average rate 1.53%, due in 2016
Debt Instrument [Line Items]
Maximum borrowing capacity of line of credit facility	1,000,000,000
Senior letters of credit facility, committed to outstanding letters of credit	149,000,000	157,600,000
Senior letters of credit facility, unused portion	675,000,000	616,500,000
$100 million Private Placement notes 5.64%, due in 2015
Debt Instrument [Line Items]
Long-term debt, face amount	100,000,000
$175 million Private Placement notes 3.89%, due in 2017
Debt Instrument [Line Items]
Long-term debt, face amount	175,000,000
$225 million Private Placement notes 4.47%, due in 2020
Debt Instrument [Line Items]
Long-term debt, face amount	225,000,000
$125 million Private Placement notes 3.26%, due in 2022
Debt Instrument [Line Items]
Long-term debt, face amount	125,000,000
Other Assets [Member]
Debt Instrument [Line Items]
Loan receivable from customer	$ 15,500,000