Summary of Significant Accounting Policies - Narrative (Details) $ in Millions		3 Months Ended
	Jan. 01, 2019 USD ($)	Mar. 31, 2019 segment	Mar. 31, 2018 USD ($)
Accounting Policies [Abstract]
Number of operating segments | segment		2
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adoption of accounting standards			$ 40
Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adoption of accounting standards			$ 40
Right-of-Use Assets [Member] | Accounting Standards Update 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adoption of accounting standards	$ 129
Lease Obligations [Member] | Accounting Standards Update 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adoption of accounting standards	$ 144