Business, Basis of Presentation and Significant Accounting Policies - Narrative (Details) $ in Millions	6 Months Ended
	Jun. 30, 2019 USD ($) segment Subsidiary	Mar. 31, 2019 USD ($)
Schedule of Equity Transactions [Line Items]
number of non-insurance subsidiaries | Subsidiary	1
Number of Operating Segments | segment	1
Accounting Standards Update 2018-02
Schedule of Equity Transactions [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	$ 0	$ 0
Accumulated Other Comprehensive Income (Loss) | Accounting Standards Update 2018-02
Schedule of Equity Transactions [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	137	0
Retained Earnings (Deficit) | Accounting Standards Update 2018-02
Schedule of Equity Transactions [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	$ (137)	$ 0
Discontinued Operations, Held-for-sale | Directed Services LLC (DSL)
Schedule of Equity Transactions [Line Items]
Discontinued Operation, Equity Method Investment Retained after Disposal, Ownership Interest after Disposal	9.99%