Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2018

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)
2018
Operating revenue	$	5,945	5,902	5,818	5,778		23,443
Operating income (loss)	750		767	894	(1,841	)	570
Net income (loss)	115		292	272	(2,412	)	(1,733	)
Basic earnings (loss) per common share	0.11		0.27	0.25	(2.26	)	(1.63	)
Diluted earnings (loss) per common share	0.11		0.27	0.25	(2.26	)	(1.63	)
2017
Operating revenue	$	4,209	4,090	4,034	5,323		17,656
Operating income	631		367	487	524		2,009
Net income	163		17	92	1,117		1,389
Basic earnings per common share	0.30		0.03	0.17	1.26		2.21
Diluted earnings per common share	0.30		0.03	0.17	1.26		2.21