Condensed Consolidated Statements of Changes in Shareholder's Equity - USD ($) $ in Millions	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings (Deficit)
Beginning Balance at Dec. 31, 2016	$ 3,377	$ 3	$ 2,994	$ 560	$ (180)
Comprehensive income (loss):
Net income (loss)	40	0	0	0	40
Other comprehensive income (loss), after tax	231	0	0	231	0
Comprehensive income (loss)	271
Dividends paid and distributions of capital	(261)	0	(261)	0	0
Employee related benefits	1	0	1	0	0
Ending Balance at Sep. 30, 2017	3,388	3	2,734	791	(140)
Increase (Decrease) in Stockholders' Equity
Cumulative Effect of New Accounting Principle in Period of Adoption | Accounting Standards Update 2014-09	72	0	0	0	72
Cumulative Effect of New Accounting Principle in Period of Adoption | Accounting Standards Update 2016-01	0	0	0	(12)	12
Beginning Balance (Scenario, Previously Reported) at Dec. 31, 2017	3,581	3	2,730	818	30
Beginning Balance at Dec. 31, 2017	3,581
Balance as adjusted at Dec. 31, 2017	3,653	3	2,730	806	114
Comprehensive income (loss):
Net income (loss)	347	0	0	0	347
Other comprehensive income (loss), after tax	(605)	0	0	(605)	0
Comprehensive income (loss)	(258)
Dividends paid and distributions of capital	(126)	0	0	0	(126)
Employee related benefits	(2)	0	(2)	0	0
Ending Balance at Sep. 30, 2018	$ 3,267	$ 3	$ 2,728	$ 201	$ 335