Accumulated Other Comprehensive Income (Loss) (Reclassification out of AOCI) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)	$ (47)	$ (22)	$ 210	$ (76)
Net change in value	2	0	0	0
Derivative Financial Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)	(7)	11	5	23
Unrealized gain (loss) on investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)	(2)	0	0	0
Income Tax Benefit (Expense) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)	0	0	330	0
Prior Service Cost [Member] | Pension And Retiree Medical Liability [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)	(48)	(54)	(154)	(162)
Actuarial Loss [Member] | Pension And Retiree Medical Liability [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)	10	21	29	63
AA [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)	(46)	(22)	209	(76)
Net change in value	2	3	2	3
Non-cash tax provision on sale of fuel hedging contracts			328
AA [Member] | Derivative Financial Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)	(7)	11	5	23
AA [Member] | Unrealized gain (loss) on investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net change in value	(2)	0	(2)	0
AA [Member] | Income Tax Benefit (Expense) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)	0	0	328	0
AA [Member] | Prior Service Cost [Member] | Pension And Retiree Medical Liability [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)	(47)	(54)	(151)	(162)
AA [Member] | Actuarial Loss [Member] | Pension And Retiree Medical Liability [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified from accumulated other comprehensive income (loss)	10	21	29	63
Fuel Hedging Contract [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Non-cash tax provision on sale of fuel hedging contracts			330
Fuel Hedging Contract [Member] | AA [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Non-cash tax provision on sale of fuel hedging contracts	$ 328		$ 328