Income Taxes (Tables)

12 Months Ended

Dec. 31, 2016

Income Tax Disclosure [Abstract]

Income tax benefit (provision)

Our income tax (provision) benefit consisted of the following:

	Year Ended December 31,
(in millions)	2016			2015			2014
Current tax (provision) benefit:
Federal	$	—		$	(23	)	$	21
State and local	(28		)	(25		)	(9		)
International	(12		)	(2		)	(11		)
Deferred tax (provision) benefit:
Federal	(2,080		)	(2,409		)	(424		)
State and local	(143		)	(172		)	10
Income tax provision	$	(2,263	)	$	(2,631	)	$	(413	)

Effective income tax rate reconcillation

The following table presents the principal reasons for the difference between the effective tax rate and the U.S. federal statutory income tax rate:

	Year Ended December 31,
	2016		2015		2014
U.S. federal statutory income tax rate	35.0	%	35.0	%	35.0	%
State taxes, net of federal benefit	1.8		1.8		2.0
Decrease in valuation allowance	—		(0.2	)	(2.4	)
Foreign tax rate differential	(2.0	)	—		—
Other	(0.7	)	0.2		3.9
Effective income tax rate	34.1	%	36.8	%	38.5	%

Deferred taxes

The following table shows significant components of our deferred tax assets and liabilities:

	December 31,
(in millions)	2016			2015
Deferred tax assets:
Net operating loss carryforwards	$	2,485		$	3,838
Pension, postretirement and other benefits	5,259			5,444
Fuel derivatives MTM adjustments	112			282
Alternative minimum tax credit carryforward	379			379
Deferred revenue	1,544			1,522
Other	963			1,047
Valuation allowance	(40		)	(56		)
Total deferred tax assets	$	10,702		$	12,456
Deferred tax liabilities:
Depreciation	$	5,701		$	5,490
Intangible assets	1,691			1,681
Other	246			329
Total deferred tax liabilities	$	7,638		$	7,500
Net deferred tax assets	$	3,064		$	4,956

Summary of valuation allowance and associated activity

The following table shows the balance of our valuation allowance and the associated activity:

(in millions)	2016			2015			2014
Valuation allowance at beginning of period	$	56		$	46		$	177
Income tax provision	—			—			(9		)
Other comprehensive income tax (provision) benefit	(16		)	24			(3		)
Expirations	—			(4		)	(91		)
Release of valuation allowance	—			(10		)	(28		)
Valuation allowance at end of period	$	40		$	56		$	46