Credit and Other Debt Agreements - Credit Agreement - Additional information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Debt acquisition costs	$ 1,300,000
Liabilities	4,775,000,000	3,693,700,000
Line of credit facility, increase in additional borrowings	890,500,000	303,000,000	151,000,000
Long-term debt	36,500,000
Credit Agreement [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	600,000,000
Number of financial institutions entered in unsecured multicurrency credit agreement	15
Debt instrument, maturity date	Sep. 19, 2018
Line of credit facility, maximum amount outstanding during period	850,000,000
Fixed rate (alternative one) over LIBOR	0.85%
Fixed rate (alternative two) over LIBOR	0.95%
Fixed rate (alternative three) over LIBOR	1.05%
Fixed rate (alternative four) over LIBOR	1.25%
Fixed rate (alternative five) over LIBOR	1.45%
Annual facility fee of revolving credit facility (alternative one)	0.15%
Annual facility fee of revolving credit facility (alternative two)	0.175%
Annual facility fee of revolving credit facility (alternative three)	0.20%
Annual facility fee of revolving credit facility (alternative four)	0.25%
Annual facility fee of revolving credit facility (alternative five)	0.30%
Debt acquisition costs	2,100,000
Estimated fair value of outstanding borrowings	530,500,000
Credit Agreement [Member] | Standby Letters of Credit [Member]
Debt Instrument [Line Items]
Long-term debt, gross	75,000,000
Line of credit facility, amount outstanding	16,000,000
Liabilities	9,000,000
Line of credit facility, fair value of amount outstanding	530,500,000
Line of credit facility, remaining borrowing capacity	53,500,000
Line of credit facility, increase in additional borrowings	53,500,000
Credit Agreement [Member] | Swing Loan [Member]
Debt Instrument [Line Items]
Long-term debt, gross	50,000,000
Previous Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	500,000,000
Debt instrument, maturity date	Jul. 14, 2014
Early termination fees incurred on termination of credit facility	0
Note Purchase Agreements [Member] | Level 3 [Member]
Debt Instrument [Line Items]
Line of credit facility, fair value of amount outstanding	979,400,000
Long-term debt	$ 925,000,000