Quarterly Financial Data (Tables)

12 Months Ended

Dec. 31, 2013

Quarterly Financial Data [Abstract]

Schedule of Quarterly Financial Information

	THREE MONTHS ENDED
(in millions except per share amounts)	March 31		June 30		Sept. 30		Dec. 31
2013
Operating revenues	$	4,084	$	4,643	$	4,545	$	4,428
Operating income	70		433		390		386
Income before income taxes	94		363		419		334
Net income	59		224		259		212
Net income per share, basic	0.08		0.31		0.37		0.30
Net income per share, diluted	0.08		0.31		0.37		0.30
	March 31		June 30		Sept. 30		Dec. 31
2012
Operating revenues	$	3,991	$	4,616	$	4,309	$	4,173
Operating income	22		460		51		91
Income (loss) before income taxes	159		368		33		125
Net income (loss)	98		228		16		78
Net income (loss) per share, basic	0.13		0.30		0.02		0.11
Net income (loss) per share, diluted	0.13		0.30		0.02		0.11