Accounting Policies - Accounting Standards Updates (Details) - Forecast - Accounting Standards Update 2016-02 $ in Millions	Jan. 01, 2019 USD ($)
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, right-of-use asset	$ 60
Operating lease, liability	60
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, right-of-use asset	70
Operating lease, liability	$ 70