Summary of Significant Accounting Policies - Recently Issued Accounting Standards (Details) - Subsequent Event - Scenario, Forecast - Accounting Standards Update 2016-02 $ in Millions	Jan. 01, 2019 USD ($)
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
ROU assets	$ 450
Lease liabilities	450
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
ROU assets	500
Lease liabilities	$ 500