QUARTERLY INTERIM FINANCIAL INFORMATION (UNAUDITED) (Details) - USD ($) $ in Millions	3 Months Ended								6 Months Ended	9 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	Jun. 30, 2017	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Data [Abstract]
Total Revenues	$ 2,442	$ 2,429	$ 4,548	$ 2,314	$ (213)	$ 2,153	$ 3,297	$ 3,901	$ 6,859	$ 9,288	$ 11,733	$ 9,138	$ 8,961
Total benefits and other deductions	2,066	2,409	2,514	2,489	1,638	2,013	2,424	2,441	5,002	7,412	9,478	8,516	7,923
Net income (loss)	$ 1,712	$ 121	$ 1,615	$ (54)	$ (1,144)	$ 175	$ 600	$ 1,075	$ 1,559	$ 1,679	$ 3,394	$ 706	$ 1,060