Income Taxes (Components of deferred tax assets and liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Components of Deferred Tax Assets [Abstract]
Reserves and allowances	$ 112	$ 107
Intangibles	0	1
Debt cancellation and other	48	58
Net operating loss and credit carryforwards	73	237
Total deferred tax assets	233	403
Components of Deferred Tax Liabilities [Abstract]
Property and equipment	(1,714)	(1,535)
Intangibles	(272)	(312)
Valuation allowance	(12)	0
Total deferred tax liability	(1,998)	(1,847)
Total deferred income tax (liability)	$ (1,765)	$ (1,444)