Schedule II. Condensed Financial Information of Registrant (Parent Company) (Schedule of Condensed Financial Information of Registrant, Statements of Operations and Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues
Net realized investment (losses) gains									$ 93	$ 50	$ (67)
Total revenues	$ 2,448	$ 2,398	$ 2,366	$ 2,330	$ 2,390	$ 2,433	$ 2,348	$ 2,195	9,542	9,366	9,101
Expenses
Interest									161	159	155
Income tax expense									(411)	(278)	(70)
Net income	$ 223	$ 144	$ 272	$ 260	$ 241	$ 343	$ 209	$ 66	899	859	479
Total comprehensive income (loss)									1,104	1,001	(236)
Parent Company
Revenues
Net investment income									6	3	1
Net realized investment (losses) gains									(42)	(7)	5
Total revenues									(36)	(4)	6
Expenses
Administrative and general									2	1	1
Interest									152	155	154
Total expenses									154	156	155
Loss from operations before income taxes and equity in net income of subsidiaries									(190)	(160)	(149)
Income tax expense									57	41	34
Loss before equity in net income of subsidiaries									(133)	(119)	(115)
Equity in net income of subsidiaries									1,032	978	594
Net income									899	859	479
Equity in other comprehensive income of subsidiaries									205	142	(715)
Total comprehensive income (loss)									$ 1,104	$ 1,001	$ (236)