Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2015

Quarterly Financial Information Disclosure [Abstract]

Schedule of quarterly financial information

	First Quarter		Second Quarter	Third Quarter	Fourth Quarter	Total
	(Dollars in millions, except per share amounts)
2015
Operating revenues	$	4,451	4,419	4,554	4,476	17,900
Operating income	649		549	656	751	2,605
Net income	192		143	205	338	878
Basic earnings per common share	0.34		0.26	0.37	0.62	1.58
Diluted earnings per common share	0.34		0.26	0.37	0.62	1.58
2014
Operating revenues	$	4,538	4,541	4,514	4,438	18,031
Operating income	653		655	619	483	2,410
Net income	203		193	188	188	772
Basic earnings per common share	0.35		0.34	0.33	0.33	1.36
Diluted earnings per common share	0.35		0.34	0.33	0.33	1.36