Debt (Details) (USD $)			12 Months Ended			12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 Short-term debt [Member]	Dec. 31, 2012 Short-term debt [Member]	Nov. 04, 2013 300 million unsecured medium-term notes due 2018 [Member]	Dec. 31, 2013 Unsecured Medium Term Notes Due 2019 [Member]	Feb. 19, 2013 Unsecured Medium Term Notes Due 2019 [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 900,000,000
Debt Instrument, Face Amount					300,000,000		250,000,000
Short-term debt and current portion of long-term debt:
Short-term debt, Weighted Average Interest Rate			1.70%	2.27%
Maturity date range, start			Jan. 01, 2014
Debt Instrument, Call Feature						101% of principal plus accrued and unpaid interest
Short-term debt	1,315,000	9,820,000
Current portion of long-term debt, including capital leases	258,123,000	358,155,000
Total short-term debt and current portion of long-term debt	$ 259,438,000	$ 367,975,000