Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (3,030)		$ (2,980)
Other comprehensive income (loss) before reclassifications	(16)
Amounts reclassified from accumulated other comprehensive income (loss)	(34)
Other Comprehensive Income (Loss), Net of Tax	(50)
Pension And Retiree Medical Liability [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(2,355)		(2,322)
Other comprehensive income (loss) before reclassifications	0
Amounts reclassified from accumulated other comprehensive income (loss)	(33)
Other Comprehensive Income (Loss), Net of Tax	(33)
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(2)		(1)
Other comprehensive income (loss) before reclassifications	(1)
Amounts reclassified from accumulated other comprehensive income (loss)	0
Other Comprehensive Income (Loss), Net of Tax	(1)
Derivative Financial Instruments [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(1)		15
Other comprehensive income (loss) before reclassifications	(15)
Amounts reclassified from accumulated other comprehensive income (loss)	(1)
Other Comprehensive Income (Loss), Net of Tax	(16)
Income Tax Benefit Expense [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(672)		(672)
Other comprehensive income (loss) before reclassifications	0
Amounts reclassified from accumulated other comprehensive income (loss)	0
Other Comprehensive Income (Loss), Net of Tax	0
Prior Service Cost [Member] | Pension And Retiree Medical Liability [Member]
Amounts reclassified from accumulated other comprehensive income (loss)	(54)	[1]
Actuarial Loss [Member] | Pension And Retiree Medical Liability [Member]
Amounts reclassified from accumulated other comprehensive income (loss)	$ 21	[1]

[1] 1These accumulated other comprehensive income components are included in the computation of net periodic pension and retiree medical costs. See Note 8 to the Condensed Consolidated Financial Statements for additional details.