QUARTERLY FINANCIAL INFORMATION (Unaudited) (Details) - USD ($) $ / shares in Units, $ 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
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 13,189	$ 13,282	$ 13,534	$ 13,762	$ 12,878	$ 13,694	$ 14,007	$ 13,800	$ 53,767	$ 54,379	$ 54,289
Income (loss) before income taxes	490	799	1,042	1,689	(486)	902	636	500	4,020	1,552	2,431
Net income	$ 184	$ 499	$ 650	$ 1,115	$ (401)	$ 450	$ 311	$ 254	$ 2,448	$ 614	$ 1,276
Basic earnings (loss) per common share (in dollars per share)	$ 1.30	$ 3.46	$ 4.49	$ 7.54	$ (2.68)	$ 3.01	$ 2.08	$ 1.70	$ 16.94	$ 4.11	$ 8.54
Diluted earnings (loss) per common share (in dollars per share)	$ 1.29	$ 3.44	$ 4.46	$ 7.49	$ (2.68)	$ 2.98	$ 2.06	$ 1.68	$ 16.81	$ 4.07	$ 8.44
Long-term insurance reserve strengthening expense					$ 505
Long-term insurance reserve strengthening expense, net of tax					$ 318
Long-term insurance reserve strengthening expense, per diluted share (in dollars per share)					$ 2.11
Premiums reduction, write off of risk corridor receivables					$ 583
Premiums reduction, write off of risk corridor receivables, net of tax										$ 367
Premiums reduction, write off of risk corridor receivables, per diluted share (in dollars per share)										$ 2.43