Income Taxes (Deferred Tax Assets and Deferred Tax Liabilities) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Deferred Tax Liabilities:
Differences between book and tax basis of property	$ (2,178)	$ (2,089)
Other taxable temporary differences	(337)	(377)
Total deferred tax liability	(2,515)	(2,466)
Deferred Tax Assets:
Operating loss carryforwards	2,108	1,592
Capital loss carryforwards	103	108
Bad debt and other book provisions	277	330
Retirement costs	291	611
Tax credit carryforwards	38	46
Other deductible temporary differences	420	512
Total gross deferred tax asset	3,237	3,199
Less: valuation allowance	(1,090)	(895)
Total net deferred tax asset	2,147	2,304
Net deferred tax asset (liability)	$ (368)	$ (162)