Summary of Significant Accounting Policies - Recently Issued and Adopted Accounting Pronouncements (Details) - USD ($) $ in Millions	Oct. 01, 2019	Sep. 30, 2019
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted		false
Change in Accounting Principle, Accounting Standards Update, Early Adoption		false
Accounting Standards Update 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted		false
Change in Accounting Principle, Accounting Standards Update, Early Adoption		false
Accounting Standards Update 2018-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted		false
Change in Accounting Principle, Accounting Standards Update, Early Adoption		false
Accounting Standards Update 2018-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted		false
Change in Accounting Principle, Accounting Standards Update, Early Adoption		false
Accounting Standards Update 2018-14
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted		false
Change in Accounting Principle, Accounting Standards Update, Early Adoption		false
Accounting Standards Update 2018-15
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted		false
Change in Accounting Principle, Accounting Standards Update, Early Adoption		false
Accounting Standards Update 2018-20
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted		false
Change in Accounting Principle, Accounting Standards Update, Early Adoption		false
Accounting Standards Update 2019-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted		false
Change in Accounting Principle, Accounting Standards Update, Early Adoption		false
Accounting Standards Update 2019-04
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted		false
Change in Accounting Principle, Accounting Standards Update, Early Adoption		false
Accounting Standards Update 2019-05
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted		false
Change in Accounting Principle, Accounting Standards Update, Early Adoption		false
Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted		true
Change in Accounting Principle, Accounting Standards Update, Adoption Date		Oct. 01, 2018
Change in Accounting Principle, Accounting Standards Update, Early Adoption		false
Change in Accounting Principle, Accounting Standards Update, Transition Option Elected		Modified Retrospective
Minimum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Lease, Right-of-Use Asset	$ 31
Operating Lease, Liability	31
Maximum
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Lease, Right-of-Use Asset	36
Operating Lease, Liability	$ 36