Debt - Narrative (Details) - USD ($)	1 Months Ended						6 Months Ended	12 Months Ended
	Feb. 28, 2018	Jan. 31, 2018	Sep. 30, 2017	Aug. 31, 2017	Mar. 31, 2016	Nov. 30, 2010	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Feb. 02, 2018
Debt Instrument [Line Items]
Issuance of long-term debt								$ 947,500,000	$ 297,600,000	$ 397,000,000
Make whole payment for extinguishment of debt								168,800,000	300,000,000	0
Loss on extinguishment of debt								0	10,100,000	0
Short-term debt							$ 56,100,000	56,100,000	68,100,000
Commercial paper							26,000,000	26,000,000	63,000,000
Line of credit outstanding, current portion									5,100,000
Interest and fees paid								59,500,000	47,900,000	$ 37,100,000
Other LOC
Debt Instrument [Line Items]
Line of credit, maximum borrowing capacity							54,800,000	54,800,000	53,900,000
Line of credit outstanding, current portion							$ 20,300,000	$ 20,300,000	$ 21,500,000
Notes 2022 Term Interest Rate Lock
Debt Instrument [Line Items]
Loss on forward interest rate lock, recorded in accumulated other comprehensive loss						$ 1,600,000
Senior Notes | Notes 2028 Term
Debt Instrument [Line Items]
Face amount	$ 450,000,000										$ 450,000,000
Interest rate, stated percentage	3.50%						3.50%	3.50%			3.50%
Issuance of long-term debt	$ 442,600,000
Senior Notes | Notes 2027 Term
Debt Instrument [Line Items]
Face amount				$ 300,000,000
Interest rate, stated percentage				3.15%			3.15%	3.15%	3.15%
Proceeds from debt, net of issuance costs				$ 294,600,000
Senior Notes | Notes 2018 Term
Debt Instrument [Line Items]
Interest rate, stated percentage			5.95%
Make whole payment for extinguishment of debt								$ 9,900,000
Debt instrument, repurchase amount			$ 300,000,000
Loss on extinguishment of debt			$ 10,100,000
Senior Notes | Notes 2026 Term
Debt Instrument [Line Items]
Face amount					$ 400,000,000
Interest rate, stated percentage					3.35%		3.35%	3.35%	3.35%
Proceeds from issuance of long-term debt					$ 393,400,000
Senior Notes | Notes 2022 Term
Debt Instrument [Line Items]
Face amount						$ 300,000,000
Interest rate, stated percentage						3.625%	3.625%	3.625%	3.625%
Line of Credit | Term Loan Agreement
Debt Instrument [Line Items]
Line of credit, maximum borrowing capacity		$ 500,000,000									$ 500,000,000
Amortization percentage, equal quarterly installments, year one											5.00%
Amortization percentage, equal quarterly installments, year two											5.00%
Amortization percentage, equal quarterly installments, year three											7.50%
Amortization percentage, equal quarterly installments, year four											10.00%
Amortization percentage, equal quarterly installments, year five											10.00%
Make whole payment for extinguishment of debt							$ 150,000,000
Line of Credit | Revolving Credit Facility | Credit Agreement
Debt Instrument [Line Items]
Line of credit, maximum borrowing capacity		$ 750,000,000
Line of credit facility covenants maximum debt to capitalization percentage		65.00%
Debt instrument, term		5 years
Line of credit facility, accordion feature, higher borrowing capacity option		$ 1,250,000,000.000