QUARTERLY FINANCIAL INFORMATION (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 14,168	$ 14,206	$ 14,259	$ 14,279	$ 13,189	$ 13,282	$ 13,534	$ 13,762	$ 56,912	$ 53,767	$ 54,379
Income (loss) before income taxes	436	901	19	707	490	799	1,042	1,689	2,063	4,020	1,552
Net income	$ 355	$ 644	$ 193	$ 491	$ 184	$ 499	$ 650	$ 1,115	$ 1,683	$ 2,448	$ 614
Basic earnings per common share (in USD per share)	$ 2.60	$ 4.68	$ 1.40	$ 3.56	$ 1.30	$ 3.46	$ 4.49	$ 7.54	$ 12.24	$ 16.94	$ 4.11
Diluted earnings per common share (in USD per share)	$ 2.58	$ 4.65	$ 1.39	$ 3.53	$ 1.29	$ 3.44	$ 4.46	$ 7.49	$ 12.16	$ 16.81	$ 4.07