Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Selected Quarterly Financial Data (Unaudited)
Total revenues	$ 410	$ 413	$ 412	$ 431	$ 418	$ 433	$ 487	$ 466	$ 1,666	$ 1,804	$ 1,257
Income (loss) from continuing operations	53	(41)	139	(68)	(485)	(309)	(52)	(27)	83	(873)	(56)
Net (income) loss from discontinued operations	(10)	16	9	11	(456)	23	15	41	26	(377)	116
Net income (loss)	$ 43	$ (25)	$ 148	$ (57)	$ (941)	$ (286)	$ (37)	$ 14	$ 109	$ (1,250)	$ 60
Basic income (loss) per common share:
Basic Income (loss) from continuing operations (in dollars per share)	$ 0.89	$ (0.69)	$ 2.33	$ (1.14)	$ (8.18)	$ (5.22)	$ (0.91)	$ (0.48)	$ 1.39	$ (15.03)	$ (1.36)
Basic income (loss) from discontinued operations, net of tax (in dollars per share)	(0.17)	0.27	0.15	0.18	(7.69)	0.39	0.26	0.73	0.44	(6.49)	2.82
Basic income (loss) per common share (in dollars per share)	0.72	(0.42)	2.48	(0.96)	(15.87)	(4.83)	(0.65)	0.25	1.83	(21.52)	1.46
Diluted income (loss) per common share:
Diluted Income (loss) from continuing operations (in dollars per share)	0.87	(0.69)	2.32	(1.14)	(8.18)	(5.22)	(0.91)	(0.48)	1.38	(15.03)	(1.36)
Diluted income (loss)from discontinued operations, net of tax (in dollars per share)	(0.17)	0.27	0.15	0.18	(7.69)	0.39	0.26	0.73	0.43	(6.49)	2.82
Diluted income (loss) per common share (in dollars per share)	$ 0.70	$ (0.42)	$ 2.47	$ (0.96)	$ (15.87)	$ (4.83)	$ (0.65)	$ 0.25	$ 1.81	$ (21.52)	$ 1.46