Supplementary Quarterly Financial Information (Unaudited) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Quarterly Financial Information Disclosure [Abstract]
Operating Revenues	$ 1,256	$ 1,457	$ 1,265	$ 1,219	$ 1,262	$ 1,542	$ 1,289	$ 1,198	$ 5,197	$ 5,291	$ 5,152
Operating Income (Loss)	225	338	202	235	172	378	265	213	1,000	1,028	1,002
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ 101	$ 180	$ 90	$ 116	$ 67	$ 195	$ 127	$ 97	$ 487	$ 486	$ 437