Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2014

Quarterly Financial Information Disclosure [Abstract]

Schedule of quarterly financial information

	First Quarter		Second Quarter	Third Quarter	Fourth Quarter	Total
	(Dollars in millions)
2014
Operating revenues	$	2,211	2,206	2,198	2,223	8,838
Operating income	542		546	528	496	2,112
Income tax expense	160		162	156	161	639
Net income	253		256	245	216	970

	First Quarter		Second Quarter	Third Quarter	Fourth Quarter	Total
	(Dollars in millions)
2013
Operating revenues	$	2,159	2,199	2,188	2,207	8,753
Operating income	553		525	493	507	2,078
Income tax expense	166		155	139	142	602
Net income	264		246	218	236	964