Business and Basis of Presentation (Details) $ in Millions	Sep. 30, 2018 Company	Dec. 31, 2017 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of holding companies having outstanding public debt | Company	2
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Effect of adoption of ASU		$ 32
Retained Earnings [Member] | Accounting Standards Update 2016-01 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Effect of adoption of ASU		$ (32)