Income Taxes (Tables)

12 Months Ended

Dec. 31, 2016

Income Tax Disclosure [Abstract]

Summary of open income tax years by jurisdiction

Our open income tax years by major jurisdiction are as follows at December 31, 2016:

Jurisdiction	Open Tax Years
Federal	2013—current
State
Arizona	2010—current
Other states	2012—current

Schedule of components of the income tax expense from continuing operations

The components of the income tax expense from continuing operations are as follows:

	Years Ended December 31,
	2016			2015		2014
	(Dollars in millions)
Income tax expense:
Current:
Federal and foreign	$	686		734		738
State and local	115			114		129
Total current	801			848		867
Deferred:
Federal and foreign	(103		)	(170	)	(209	)
State and local	(20		)	(19	)	(19	)
Total deferred	(123		)	(189	)	(228	)
Income tax expense	$	678		659		639

Schedule of effective income tax rate for continuing operations that differs from the statutory tax rate

The effective income tax rate for continuing operations differs from the statutory tax rate as follows:

	Years Ended December 31,
	2016		2015		2014
	(in percent)
Effective income tax rate:
Federal statutory income tax rate	35.0	%	35.0	%	35.0	%
State income taxes-net of federal effect	3.5	%	3.6	%	4.0	%
Other	—	%	(0.6	)%	0.7	%
Effective income tax rate	38.5	%	38.0	%	39.7	%

Schedule of components of the deferred tax assets and liabilities

The components of the deferred tax assets and liabilities are as follows:

	As of December 31,
	2016			2015
	(Dollars in millions)
Deferred tax assets and liabilities:
Deferred tax liabilities:
Property, plant and equipment	$	(1,384	)	(1,431	)
Intangibles assets	(1,088		)	(1,153	)
Receivable from an affiliate due to pension plan participation	(452		)	(460	)
Other	—			(59	)
Total deferred tax liabilities	(2,924		)	(3,103	)
Deferred tax assets:
Payable to affiliate due to post-retirement benefit plan participation	954			921
Debt premiums	—			21
Other	209			277
Total deferred tax assets	1,163			1,219
Valuation allowance on deferred tax assets	(12		)	(12	)
Net deferred tax assets	1,151			1,207
Net deferred tax liabilities	$	(1,773	)	(1,896	)