Debt (Details Textual)	9 Months Ended
	Sep. 30, 2015 USD ($) Institutions	Aug. 31, 2015 USD ($)	May. 31, 2015 USD ($)	Apr. 30, 2015 USD ($)	Feb. 28, 2015 USD ($)	Dec. 31, 2014 USD ($)
Debt Instrument [Line Items]
Aggregate notional amount of interest rate swaps	$ 825,000,000					$ 600,000,000
Number of lending institutions | Institutions	12
Maximum borrowing capacity	$ 1,200,000,000.0
Annual facility fees, percentage	0.10%
Ratio of debt to consolidated net worth	3
Debt to consolidated tangible net worth ratio	215.00%
Line of credit remaining capacity	$ 694,900,000
Current maturities classified as long-term debt	300,000,000					698,500,000
Trade receivables borrowings	0					60,000,000
Cash proceeds on financing transaction backed by a portion of revenue earning equipment	92,900,000			$ 156,400,000
Total available proceeds under trade receivables purchase and sale program	$ 175,000,000
Number of days under trade receivables purchase and sale program	364 days
Letters of credit and surety bonds outstanding	$ 339,300,000					334,300,000
Asset-backed U.S. obligations [Member]
Debt Instrument [Line Items]
Unsecured Long Term Debt Current And Noncurrent	448,331,000					218,137,000
U.S commercial paper [Member]
Debt Instrument [Line Items]
Commercial paper classified as long term debt	461,414,000					$ 276,694,000
Global Revolving Credit Facility Member
Debt Instrument [Line Items]
Current maturities classified as long-term debt	$ 41,000,000
Unsecured Medium Term Notes Due September 2020 [Member] [Member]
Debt Instrument [Line Items]
Face amount of unsecured medium-term notes issued		$ 300,000,000
Unsecured Medium Term Notes Due May 2020 [Member]
Debt Instrument [Line Items]
Face amount of unsecured medium-term notes issued			$ 300,000,000
Debt repurchase price, percentage	101.00%
Unsecured Medium Term Notes Due March 2020 [Member]
Debt Instrument [Line Items]
Face amount of unsecured medium-term notes issued					$ 400,000,000
Letter of Credit [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 75,000,000
Letter of credit outstanding amount	$ 0
Minimum [Member]
Debt Instrument [Line Items]
Annual facility fees, percentage	0.075%
Maximum [Member]
Debt Instrument [Line Items]
Annual facility fees, percentage	0.25%