Summary of Significant Accounting Policies - New Accounting Pronouncements (Details) - Accounting Standards Update 201602 - Proforma Adjustment [Member] $ in Millions	Sep. 30, 2018 USD ($)
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Initial lease liability	$ 60
Right-of-use asset	60
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Initial lease liability	80
Right-of-use asset	$ 80