Condensed Financial Information of Registrant - Condensed Statements of Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	$ 201	$ 197	$ 202	$ 107	$ (262)	$ (97)	$ (230)	$ 77	$ 707	$ (512)	$ 52
Unrealized investment (loss) gain									(3)	(5)	3
Less: effect of income taxes									(1)	(2)	1
Other comprehensive (loss) income, net of tax									(2)	(3)	2
Comprehensive income (loss)									705	(515)	54
Parent Company
Condensed Financial Statements, Captions [Line Items]
Net income (loss)									707	(512)	52
Unrealized investment (loss) gain									(3)	(5)	3
Less: effect of income taxes									(1)	(2)	1
Other comprehensive (loss) income, net of tax									(2)	(3)	2
Comprehensive income (loss)									$ 705	$ (515)	$ 54