QUARTERLY FINANCIAL INFORMATION (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 13,361	$ 13,363	$ 13,732	$ 13,833	$ 12,328	$ 12,238	$ 12,222	$ 11,712	$ 54,289	$ 48,500	$ 41,313
Income before income taxes	246	648	793	744	287	551	646	686	2,431	2,170	1,921
Net income	$ 101	$ 314	$ 431	$ 430	$ 145	$ 290	$ 344	$ 368	$ 1,276	$ 1,147	$ 1,231
Basic earnings per common share (in dollars per share)	$ 0.68	$ 2.11	$ 2.88	$ 2.86	$ 0.96	$ 1.87	$ 2.22	$ 2.37	$ 8.54	$ 7.44	$ 7.81
Diluted earnings per common share (in dollars per share)	$ 0.67	$ 2.09	$ 2.85	$ 2.82	$ 0.94	$ 1.85	$ 2.19	$ 2.35	$ 8.44	$ 7.36	$ 7.73
Provision for premium deficiency	$ 176								$ 176	$ 0	$ 0
Provision for premium deficiency, net	$ 112
Provision for premium deficiency, per diluted share	$ 0.74