SUPPLEMENTARY DATA QUARTERLY FINANCIAL DATA - UNAUDITED - 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
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 5,371	$ 5,284	$ 5,305	$ 5,012	$ 5,289	$ 5,051	$ 5,409	$ 5,009	$ 20,972	$ 20,758	$ 20,452
Operating income	274	607	409	510	422	596	818	530	1,800	2,366	2,504
Net income	$ 279	$ 387	$ 232	$ 375	$ 317	$ 503	$ 667	$ 420	$ 1,273	$ 1,907	$ 1,459
Basic earnings per share (in USD per share)	$ 0.85	$ 1.17	$ 0.70	$ 1.10	$ 0.93	$ 1.45	$ 1.89	$ 1.17	$ 3.83	$ 5.45	$ 3.89
Diluted earnings per share (in USD per share)	$ 0.85	$ 1.16	$ 0.69	$ 1.09	$ 0.92	$ 1.43	$ 1.87	$ 1.16	$ 3.80	$ 5.38	$ 3.84