Debt - Senior Secured Credit Facilities - Narrative (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Line of Credit Facility [Line Items]
Repayment of outstanding borrowings		$ 150,000,000	$ 0
Senior Secured Term Loan Facility [Member]
Line of Credit Facility [Line Items]
Debt instrument term		7 years
Repayment of outstanding borrowings	$ 3,000,000	$ 10,000,000
Senior Secured Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Debt instrument term		5 years
Line of credit facility, maximum borrowing capacity	800,000,000	$ 800,000,000
Long-term debt	0	0		$ 0
Repayment of outstanding borrowings	150,000,000
Letters of credit outstanding	$ 103,000,000	$ 103,000,000		$ 104,000,000
Commitment fee percentage		0.15%
Dollar Term Loan [Member]
Line of Credit Facility [Line Items]
Effective interest rates on senior secured term loan	3.80%	3.80%
Euro Term Loan [Member]
Line of Credit Facility [Line Items]
Effective interest rates on senior secured term loan	2.50%	2.50%