Business and Basis of Presentation (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($) Company
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of holding companies having outstanding public debt | Company	2
Retained Earnings [Member] | Accounting Standards Update 2016-01 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New accounting pronouncement or change in accounting principle, effect of change on net income | $	$ 32