QUARTERLY FINANCIAL DATA (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010
Quarterly Financial Data [Abstract]
Operating revenues	$ 4,108	$ 4,311	$ 4,136	$ 3,103	$ 3,114	$ 3,192	$ 3,168	$ 2,630
Operating income (Loss)	147	225	207	114	216	355	363	54
Income (loss) before income taxes	255	(226)	275	18	213	332	184	17
Net Income (loss)	$ 152	$ (140)	$ 161	$ 5	$ 131	$ 205	$ 112	$ 11
Net income per share, basic (in dollars per share)	$ 0.20	$ (0.18)	$ 0.21	$ 0.01	$ 0.18	$ 0.27	$ 0.15	$ 0.01
Net income per share, diluted (in dollars per share)	$ 0.20	$ (0.18)	$ 0.21	$ 0.01	$ 0.18	$ 0.27	$ 0.15	$ 0.01